Returns `true` if the provided predicate function returns `true` for all elements in a collection, `false` otherwise.

Use Array.prototype.every() to test if all elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.

Code

const all = (arr, fn = Boolean) => arr.every(fn);

Example

all([4, 2, 3], x => x > 1); // true
all([1, 2, 3]); // true

Check if all elements in an array are equal.

Use Array.prototype.every() to check if all the elements of the array are the same as the first one.

Code

const allEqual = arr => arr.every(val => val === arr[0]);

Example

allEqual([1, 2, 3, 4, 5, 6]); // false
allEqual([1, 1, 1, 1]); // true

Returns `true` if the provided predicate function returns `true` for at least one element in a collection, `false` otherwise.

Use Array.prototype.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.

Code

const any = (arr, fn = Boolean) => arr.some(fn);

Example

any([0, 1, 2, 0], x => x >= 2); // true
any([0, 0, 1, 0]); // true

Converts a 2D array to a comma-separated values (CSV) string.

Use Array.prototype.map() and Array.prototype.join(delimiter) to combine individual 1D arrays (rows) into strings. Use Array.prototype.join('\n') to combine all rows into a CSV string, separating each row with a newline. Omit the second argument, delimiter, to use a default delimiter of ,.

Code

const arrayToCSV = (arr, delimiter = ',') =>
 arr.map(v => v.map(x => `"${x}"`).join(delimiter)).join('\n');

Example

arrayToCSV([['a', 'b'], ['c', 'd']]); // '"a","b"\n"c","d"'
arrayToCSV([['a', 'b'], ['c', 'd']], ';'); // '"a";"b"\n"c";"d"'

Splits values into two groups. If an element in `filter` is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.

Use Array.prototype.reduce() and Array.prototype.push() to add elements to groups, based on filter.

Code

const bifurcate = (arr, filter) =>
 arr.reduce((acc, val, i) => (acc[filter[i] ? 0 : 1].push(val), acc), [[], []]);

Example

bifurcate(['beep', 'boop', 'foo', 'bar'], [true, true, false, true]); // [ ['beep', 'boop', 'bar'], ['foo'] ]

Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If the predicate function returns a truthy value, the collection element belongs to the first group; otherwise, it belongs to the second group.

Use Array.prototype.reduce() and Array.prototype.push() to add elements to groups, based on the value returned by fn for each element.

Code

const bifurcateBy = (arr, fn) =>
 arr.reduce((acc, val, i) => (acc[fn(val, i) ? 0 : 1].push(val), acc), [[], []]);

Example

bifurcateBy(['beep', 'boop', 'foo', 'bar'], x => x[0] === 'b'); // [ ['beep', 'boop', 'bar'], ['foo'] ]

Chunks an array into smaller arrays of a specified size.

Use Array.from() to create a new array, that fits the number of chunks that will be produced. Use Array.prototype.slice() to map each element of the new array to a chunk the length of size. If the original array can't be split evenly, the final chunk will contain the remaining elements.

Code

const chunk = (arr, size) =>
 Array.from({ length: Math.ceil(arr.length / size) }, (v, i) =>
   arr.slice(i * size, i * size + size)
 );

Example

chunk([1, 2, 3, 4, 5], 2); // [[1,2],[3,4],[5]]

Removes falsey values from an array.

Use Array.prototype.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).

Code

const compact = arr => arr.filter(Boolean);

Example

compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ]

Groups the elements of an array based on the given function and returns the count of elements in each group.

Use Array.prototype.map() to map the values of an array to a function or property name. Use Array.prototype.reduce() to create an object, where the keys are produced from the mapped results.

Code

const countBy = (arr, fn) =>
 arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
   acc[val] = (acc[val] || 0) + 1;
   return acc;
 }, {});

Example

countBy([6.1, 4.2, 6.3], Math.floor); // {4: 1, 6: 2}
countBy(['one', 'two', 'three'], 'length'); // {3: 2, 5: 1}

Counts the occurrences of a value in an array.

Use Array.prototype.reduce() to increment a counter each time you encounter the specific value inside the array.

Code

const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);

Example

countOccurrences([1, 1, 2, 1, 2, 3], 1); // 3

Deep flattens an array.

Use recursion. Use Array.prototype.concat() with an empty array ([]) and the spread operator (...) to flatten an array. Recursively flatten each element that is an array.

Code

const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));

Example

deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]

Returns the difference between two arrays.

Create a Set from b, then use Array.prototype.filter() on a to only keep values not contained in b.

Code

const difference = (a, b) => {
 const s = new Set(b);
 return a.filter(x => !s.has(x));
};

Example

difference([1, 2, 3], [1, 2, 4]); // [3]

Returns the difference between two arrays, after applying the provided function to each array element of both.

Create a Set by applying fn to each element in b, then use Array.prototype.filter() in combination with fn on a to only keep values not contained in the previously created set.

Code

const differenceBy = (a, b, fn) => {
 const s = new Set(b.map(v => fn(v)));
 return a.filter(x => !s.has(fn(x)));
};

Example

differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]
differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]

Filters out all values from an array for which the comparator function does not return `true`.

Use Array.prototype.filter() and Array.prototype.findIndex() to find the appropriate values.

Code

const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1);

Example

differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2]

Returns a new array with `n` elements removed from the left.

Use Array.prototype.slice() to slice the remove the specified number of elements from the left.

Code

const drop = (arr, n = 1) => arr.slice(n);

Example

drop([1, 2, 3]); // [2,3]
drop([1, 2, 3], 2); // [3]
drop([1, 2, 3], 42); // []

Returns a new array with `n` elements removed from the right.

Use Array.prototype.slice() to slice the remove the specified number of elements from the right.

Code

const dropRight = (arr, n = 1) => arr.slice(0, -n);

Example

dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []

Removes elements from the end of an array until the passed function returns `true`. Returns the remaining elements in the array.

Loop through the array, using Array.prototype.slice() to drop the last element of the array until the returned value from the function is true. Returns the remaining elements.

Code

const dropRightWhile = (arr, func) => {
 while (arr.length > 0 && !func(arr[arr.length - 1])) arr = arr.slice(0, -1);
 return arr;
};

Example

dropRightWhile([1, 2, 3, 4], n => n < 3); // [1, 2]

Removes elements in an array until the passed function returns `true`. Returns the remaining elements in the array.

Loop through the array, using Array.prototype.slice() to drop the first element of the array until the returned value from the function is true. Returns the remaining elements.

Code

const dropWhile = (arr, func) => {
 while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
 return arr;
};

Example

dropWhile([1, 2, 3, 4], n => n >= 3); // [3,4]

Returns every nth element in an array.

Use Array.prototype.filter() to create a new array that contains every nth element of a given array.

Code

const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);

Example

everyNth([1, 2, 3, 4, 5, 6], 2); // [ 2, 4, 6 ]

Filters out the non-unique values in an array.

Use Array.prototype.filter() for an array containing only the unique values.

Code

const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));

Example

filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]

Filters out the non-unique values in an array, based on a provided comparator function.

Use Array.prototype.filter() and Array.prototype.every() for an array containing only the unique values, based on the comparator function, fn. The comparator function takes four arguments: the values of the two elements being compared and their indexes.

Code

const filterNonUniqueBy = (arr, fn) =>
 arr.filter((v, i) => arr.every((x, j) => (i === j) === fn(v, x, i, j)));

Example

filterNonUniqueBy(
 [
   { id: 0, value: 'a' },
   { id: 1, value: 'b' },
   { id: 2, value: 'c' },
   { id: 1, value: 'd' },
   { id: 0, value: 'e' }
 ],
 (a, b) => a.id == b.id
); // [ { id: 2, value: 'c' } ]

Returns the last element for which the provided function returns a truthy value.

Use Array.prototype.filter() to remove elements for which fn returns falsey values, Array.prototype.pop() to get the last one.

Code

const findLast = (arr, fn) => arr.filter(fn).pop();

Example

findLast([1, 2, 3, 4], n => n % 2 === 1); // 3

Returns the index of the last element for which the provided function returns a truthy value.

Use Array.prototype.map() to map each element to an array with its index and value. Use Array.prototype.filter() to remove elements for which fn returns falsey values, Array.prototype.pop() to get the last one.

Code

const findLastIndex = (arr, fn) =>
 arr
   .map((val, i) => [i, val])
   .filter(([i, val]) => fn(val, i, arr))
   .pop()[0];

Example

findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)

Flattens an array up to the specified depth.

Use recursion, decrementing depth by 1 for each level of depth. Use Array.prototype.reduce() and Array.prototype.concat() to merge elements or arrays. Base case, for depth equal to 1 stops recursion. Omit the second argument, depth to flatten only to a depth of 1 (single flatten).

Code

const flatten = (arr, depth = 1) =>
 arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);

Example

flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]

Executes a provided function once for each array element, starting from the array's last element.

Use Array.prototype.slice(0) to clone the given array, Array.prototype.reverse() to reverse it and Array.prototype.forEach() to iterate over the reversed array.

Code

const forEachRight = (arr, callback) =>
 arr
   .slice(0)
   .reverse()
   .forEach(callback);

Example

forEachRight([1, 2, 3, 4], val => console.log(val)); // '4', '3', '2', '1'

Groups the elements of an array based on the given function.

Use Array.prototype.map() to map the values of an array to a function or property name. Use Array.prototype.reduce() to create an object, where the keys are produced from the mapped results.

Code

const groupBy = (arr, fn) =>
 arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
   acc[val] = (acc[val] || []).concat(arr[i]);
   return acc;
 }, {});

Example

groupBy([6.1, 4.2, 6.3], Math.floor); // {4: [4.2], 6: [6.1, 6.3]}
groupBy(['one', 'two', 'three'], 'length'); // {3: ['one', 'two'], 5: ['three']}

Returns the head of a list.

Use arr[0] to return the first element of the passed array.

Code

const head = arr => arr[0];

Example

head([1, 2, 3]); // 1

Returns all indices of `val` in an array.

If val never occurs, returns [].

Use Array.prototype.reduce() to loop over elements and store indices for matching elements. Return the array of indices.

Code

const indexOfAll = (arr, val) => arr.reduce((acc, el, i) => (el === val ? [...acc, i] : acc), []);

Example

indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4); // []

Returns all the elements of an array except the last one.

Use arr.slice(0,-1) to return all but the last element of the array.

Code

const initial = arr => arr.slice(0, -1);

Example

initial([1, 2, 3]); // [1,2]

Initializes a 2D array of given width and height and value.

Use Array.prototype.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.

Code

const initialize2DArray = (w, h, val = null) =>
 Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val));

Example

initialize2DArray(2, 2, 0); // [[0,0], [0,0]]

Initializes an array containing the numbers in the specified range where `start` and `end` are inclusive with their common difference `step`.

Use Array.from() to create an array of the desired length, (end - start + 1)/step, and a map function to fill it with the desired values in the given range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.

Code

const initializeArrayWithRange = (end, start = 0, step = 1) =>
 Array.from({ length: Math.ceil((end - start + 1) / step) }, (v, i) => i * step + start);

Example

initializeArrayWithRange(5); // [0,1,2,3,4,5]
initializeArrayWithRange(7, 3); // [3,4,5,6,7]
initializeArrayWithRange(9, 0, 2); // [0,2,4,6,8]

Initializes an array containing the numbers in the specified range (in reverse) where `start` and `end` are inclusive with their common difference `step`.

Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.prototype.map() to fill with the desired values in a range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.

Code

const initializeArrayWithRangeRight = (end, start = 0, step = 1) =>
 Array.from({ length: Math.ceil((end + 1 - start) / step) }).map(
   (v, i, arr) => (arr.length - i - 1) * step + start
 );

Example

initializeArrayWithRangeRight(5); // [5,4,3,2,1,0]
initializeArrayWithRangeRight(7, 3); // [7,6,5,4,3]
initializeArrayWithRangeRight(9, 0, 2); // [8,6,4,2,0]

Initializes and fills an array with the specified values.

Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit val to use a default value of 0.

Code

const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);

Example

initializeArrayWithValues(5, 2); // [2, 2, 2, 2, 2]

Create a n-dimensional array with given value.

Use recursion. Use Array.prototype.map() to generate rows where each is a new array initialized using initializeNDArray.

Code

const initializeNDArray = (val, ...args) =>
 args.length === 0
   ? val
   : Array.from({ length: args[0] }).map(() => initializeNDArray(val, ...args.slice(1)));

Example

initializeNDArray(1, 3); // [1,1,1]
initializeNDArray(5, 2, 2, 2); // [[[5,5],[5,5]],[[5,5],[5,5]]]

Returns a list of elements that exist in both arrays.

Create a Set from b, then use Array.prototype.filter() on a to only keep values contained in b.

Code

const intersection = (a, b) => {
 const s = new Set(b);
 return a.filter(x => s.has(x));
};

Example

intersection([1, 2, 3], [4, 3, 2]); // [2, 3]

Returns a list of elements that exist in both arrays, after applying the provided function to each array element of both.

Create a Set by applying fn to all elements in b, then use Array.prototype.filter() on a to only keep elements, which produce values contained in b when fn is applied to them.

Code

const intersectionBy = (a, b, fn) => {
 const s = new Set(b.map(fn));
 return a.filter(x => s.has(fn(x)));
};

Example

intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]

Returns a list of elements that exist in both arrays, using a provided comparator function.

Use Array.prototype.filter() and Array.prototype.findIndex() in combination with the provided comparator to determine intersecting values.

Code

const intersectionWith = (a, b, comp) => a.filter(x => b.findIndex(y => comp(x, y)) !== -1);

Example

intersectionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1.5, 3, 0]

Returns `1` if the array is sorted in ascending order, `-1` if it is sorted in descending order or `0` if it is not sorted.

Calculate the ordering direction for the first two elements. Use Object.entries() to loop over array objects and compare them in pairs. Return 0 if the direction changes or the direction if the last element is reached.

Code

const isSorted = arr => {
 let direction = -(arr[0] - arr[1]);
 for (let [i, val] of arr.entries()) {
   direction = !direction ? -(arr[i - 1] - arr[i]) : direction;
   if (i === arr.length - 1) return !direction ? 0 : direction;
   else if ((val - arr[i + 1]) * direction > 0) return 0;
 }
};

Example

isSorted([0, 1, 2, 2]); // 1
isSorted([4, 3, 2]); // -1
isSorted([4, 3, 5]); // 0

Joins all elements of an array into a string and returns this string.

Uses a separator and an end separator.

Use Array.prototype.reduce() to combine elements into a string. Omit the second argument, separator, to use a default separator of ','. Omit the third argument, end, to use the same value as separator by default.

Code

const join = (arr, separator = ',', end = separator) =>
 arr.reduce(
   (acc, val, i) =>
     i === arr.length - 2
       ? acc + val + end
       : i === arr.length - 1
         ? acc + val
         : acc + val + separator,
   ''
 );

Example

join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'); // "pen,pineapple,apple&pen"
join(['pen', 'pineapple', 'apple', 'pen'], ','); // "pen,pineapple,apple,pen"
join(['pen', 'pineapple', 'apple', 'pen']); // "pen,pineapple,apple,pen"

Converts an array of objects to a comma-separated values (CSV) string that contains only the `columns` specified.

Use Array.prototype.join(demiliter) to combine all the names in columns to create the first row. Use Array.prototype.map() and Array.prototype.reduce() to create a row for each object, substituting non-existent values with empty strings and only mapping values in columns. Use Array.prototype.join('\n') to combine all rows into a string. Omit the third argument, delimiter, to use a default delimiter of ,.

Code

const JSONtoCSV = (arr, columns, delimiter = ',') =>
 [
   columns.join(delimiter),
   ...arr.map(obj =>
     columns.reduce(
       (acc, key) => `${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`,
       ''
     )
   )
 ].join('\n');

Example

JSONtoCSV([{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }], ['a', 'b']); // 'a,b\n"1","2"\n"3","4"\n"6",""\n"","7"'
JSONtoCSV([{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }], ['a', 'b'], ';'); // 'a;b\n"1";"2"\n"3";"4"\n"6";""\n"";"7"'

Returns the last element in an array.

Use arr.length - 1 to compute the index of the last element of the given array and returning it.

Code

const last = arr => arr[arr.length - 1];

Example

last([1, 2, 3]); // 3

Takes any number of iterable objects or objects with a `length` property and returns the longest one.

If multiple objects have the same length, the first one will be returned. Returns undefined if no arguments are provided.

Use Array.prototype.reduce(), comparing the length of objects to find the longest one.

Code

const longestItem = (val, ...vals) =>
 [val, ...vals].reduce((a, x) => (x.length > a.length ? x : a));

Example

longestItem('this', 'is', 'a', 'testcase'); // 'testcase'
longestItem(...['a', 'ab', 'abc']); // 'abc'
longestItem(...['a', 'ab', 'abc'], 'abcd'); // 'abcd'
longestItem([1, 2, 3], [1, 2], [1, 2, 3, 4, 5]); // [1, 2, 3, 4, 5]
longestItem([1, 2, 3], 'foobar'); // 'foobar'

Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.

Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).

Code

const mapObject = (arr, fn) =>
 (a => (
   (a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {})
 ))();

Example

const squareIt = arr => mapObject(arr, a => a * a);
squareIt([1, 2, 3]); // { 1: 1, 2: 4, 3: 9 }

Returns the `n` maximum elements from the provided array.

If n is greater than or equal to the provided array's length, then return the original array (sorted in descending order).

Use Array.prototype.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.prototype.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.

Code

const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);

Example

maxN([1, 2, 3]); // [3]
maxN([1, 2, 3], 2); // [3,2]

Returns the `n` minimum elements from the provided array.

If n is greater than or equal to the provided array's length, then return the original array (sorted in ascending order).

Use Array.prototype.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in ascending order. Use Array.prototype.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.

Code

const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);

Example

minN([1, 2, 3]); // [1]
minN([1, 2, 3], 2); // [1,2]

Returns `true` if the provided predicate function returns `false` for all elements in a collection, `false` otherwise.

Use Array.prototype.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.

Code

const none = (arr, fn = Boolean) => !arr.some(fn);

Example

none([0, 1, 3, 0], x => x == 2); // true
none([0, 0, 0]); // true

Returns the nth element of an array.

Use Array.prototype.slice() to get an array containing the nth element at the first place. If the index is out of bounds, return undefined. Omit the second argument, n, to get the first element of the array.

Code

const nthElement = (arr, n = 0) => (n === -1 ? arr.slice(n) : arr.slice(n, n + 1))[0];

Example

nthElement(['a', 'b', 'c'], 1); // 'b'
nthElement(['a', 'b', 'b'], -3); // 'a'

Moves the specified amount of elements to the end of the array.

Use Array.prototype.slice() twice to get the elements after the specified index and the elements before that. Use the spread operator(...) to combine the two into one array. If offset is negative, the elements will be moved from end to start.

Code

const offset = (arr, offset) => [...arr.slice(offset), ...arr.slice(0, offset)];

Example

offset([1, 2, 3, 4, 5], 2); // [3, 4, 5, 1, 2]
offset([1, 2, 3, 4, 5], -2); // [4, 5, 1, 2, 3]

Groups the elements into two arrays, depending on the provided function's truthiness for each element.

Use Array.prototype.reduce() to create an array of two arrays. Use Array.prototype.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.

Code

const partition = (arr, fn) =>
 arr.reduce(
   (acc, val, i, arr) => {
     acc[fn(val, i, arr) ? 0 : 1].push(val);
     return acc;
   },
   [[], []]
 );

Example

const users = [{ user: 'barney', age: 36, active: false }, { user: 'fred', age: 40, active: true }];
partition(users, o => o.active); // [[{ 'user': 'fred',    'age': 40, 'active': true }],[{ 'user': 'barney',  'age': 36, 'active': false }]]

⚠️ WARNING: This function's execution time increases exponentially with each array element. Anything more than 8 to 10 entries will cause your browser to hang as it tries to solve all the different combinations.

Generates all permutations of an array's elements (contains duplicates).

Use recursion. For each element in the given array, create all the partial permutations for the rest of its elements. Use Array.prototype.map() to combine the element with each partial permutation, then Array.prototype.reduce() to combine all permutations in one array. Base cases are for array length equal to 2 or 1.

Code

const permutations = arr => {
 if (arr.length <= 2) return arr.length === 2 ? [arr, [arr[1], arr[0]]] : arr;
 return arr.reduce(
   (acc, item, i) =>
     acc.concat(
       permutations([...arr.slice(0, i), ...arr.slice(i + 1)]).map(val => [item, ...val])
     ),
   []
 );
};

Example

permutations([1, 33, 5]); // [ [ 1, 33, 5 ], [ 1, 5, 33 ], [ 33, 1, 5 ], [ 33, 5, 1 ], [ 5, 1, 33 ], [ 5, 33, 1 ] ]

Mutates the original array to filter out the values specified.

Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed. Use Array.prototype.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.prototype.push() to re-populate it with only the pulled values.

(For a snippet that does not mutate the original array see without)

Code

const pull = (arr, ...args) => {
 let argState = Array.isArray(args[0]) ? args[0] : args;
 let pulled = arr.filter((v, i) => !argState.includes(v));
 arr.length = 0;
 pulled.forEach(v => arr.push(v));
};

Example

let myArray = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray, 'a', 'c'); // myArray = [ 'b', 'b' ]

Mutates the original array to filter out the values at the specified indexes.

Code

const pullAtIndex = (arr, pullArr) => {
 let removed = [];
 let pulled = arr
   .map((v, i) => (pullArr.includes(i) ? removed.push(v) : v))
   .filter((v, i) => !pullArr.includes(i));
 arr.length = 0;
 pulled.forEach(v => arr.push(v));
 return removed;
};

Example

let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtIndex(myArray, [1, 3]); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]

Mutates the original array to filter out the values specified. Returns the removed elements.

Code

const pullAtValue = (arr, pullArr) => {
 let removed = [],
   pushToRemove = arr.forEach((v, i) => (pullArr.includes(v) ? removed.push(v) : v)),
   mutateTo = arr.filter((v, i) => !pullArr.includes(v));
 arr.length = 0;
 mutateTo.forEach(v => arr.push(v));
 return removed;
};

Example

let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtValue(myArray, ['b', 'd']); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]

Mutates the original array to filter out the values specified, based on a given iterator function.

Check if the last argument provided in a function. Use Array.prototype.map() to apply the iterator function fn to all array elements. Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed. Use Array.prototype.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.prototype.push() to re-populate it with only the pulled values.

Code

const pullBy = (arr, ...args) => {
 const length = args.length;
 let fn = length > 1 ? args[length - 1] : undefined;
 fn = typeof fn == 'function' ? (args.pop(), fn) : undefined;
 let argState = (Array.isArray(args[0]) ? args[0] : args).map(val => fn(val));
 let pulled = arr.filter((v, i) => !argState.includes(fn(v)));
 arr.length = 0;
 pulled.forEach(v => arr.push(v));
};

Example

var myArray = [{ x: 1 }, { x: 2 }, { x: 3 }, { x: 1 }];
pullBy(myArray, [{ x: 1 }, { x: 3 }], o => o.x); // myArray = [{ x: 2 }]

Filter an array of objects based on a condition while also filtering out unspecified keys.

Use Array.prototype.filter() to filter the array based on the predicate fn so that it returns the objects for which the condition returned a truthy value. On the filtered array, use Array.prototype.map() to return the new object using Array.prototype.reduce() to filter out the keys which were not supplied as the keys argument.

Code

const reducedFilter = (data, keys, fn) =>
 data.filter(fn).map(el =>
   keys.reduce((acc, key) => {
     acc[key] = el[key];
     return acc;
   }, {})
 );

Example

const data = [
 {
   id: 1,
   name: 'john',
   age: 24
 },
 {
   id: 2,
   name: 'mike',
   age: 50
 }
];

reducedFilter(data, ['id', 'name'], item => item.age > 24); // [{ id: 2, name: 'mike'}]

Applies a function against an accumulator and each element in the array (from left to right), returning an array of successively reduced values.

Use Array.prototype.reduce() to apply the given function to the given array, storing each new result.

Code

const reduceSuccessive = (arr, fn, acc) =>
 arr.reduce((res, val, i, arr) => (res.push(fn(res.slice(-1)[0], val, i, arr)), res), [acc]);

Example

reduceSuccessive([1, 2, 3, 4, 5, 6], (acc, val) => acc + val, 0); // [0, 1, 3, 6, 10, 15, 21]

Returns the minimum/maximum value of an array, after applying the provided function to set comparing rule.

Use Array.prototype.reduce() in combination with the comparator function to get the appropriate element in the array. You can omit the second parameter, comparator, to use the default one that returns the minimum element in the array.

Code

const reduceWhich = (arr, comparator = (a, b) => a - b) =>
 arr.reduce((a, b) => (comparator(a, b) >= 0 ? b : a));

Example

reduceWhich([1, 3, 2]); // 1
reduceWhich([1, 3, 2], (a, b) => b - a); // 3
reduceWhich(
 [{ name: 'Tom', age: 12 }, { name: 'Jack', age: 18 }, { name: 'Lucy', age: 9 }],
 (a, b) => a.age - b.age
); // {name: "Lucy", age: 9}

Takes a predicate and array, like `Array.prototype.filter()`, but only keeps `x` if `pred(x) === false`.

Code

const reject = (pred, array) => array.filter((...args) => !pred(...args));

Example

reject(x => x % 2 === 0, [1, 2, 3, 4, 5]); // [1, 3, 5]
reject(word => word.length > 4, ['Apple', 'Pear', 'Kiwi', 'Banana']); // ['Pear', 'Kiwi']

Removes elements from an array for which the given function returns `false`.

Use Array.prototype.filter() to find array elements that return truthy values and Array.prototype.reduce() to remove elements using Array.prototype.splice(). The func is invoked with three arguments (value, index, array).

Code

const remove = (arr, func) =>
 Array.isArray(arr)
   ? arr.filter(func).reduce((acc, val) => {
       arr.splice(arr.indexOf(val), 1);
       return acc.concat(val);
     }, [])
   : [];

Example

remove([1, 2, 3, 4], n => n % 2 === 0); // [2, 4]

Returns a random element from an array.

Use Math.random() to generate a random number, multiply it by length and round it of to the nearest whole number using Math.floor(). This method also works with strings.

Code

const sample = arr => arr[Math.floor(Math.random() * arr.length)];

Example

sample([3, 7, 9, 11]); // 9

Gets `n` random elements at unique keys from `array` up to the size of `array`.

Shuffle the array using the Fisher-Yates algorithm. Use Array.prototype.slice() to get the first n elements. Omit the second argument, n to get only one element at random from the array.

Code

const sampleSize = ([...arr], n = 1) => {
 let m = arr.length;
 while (m) {
   const i = Math.floor(Math.random() * m--);
   [arr[m], arr[i]] = [arr[i], arr[m]];
 }
 return arr.slice(0, n);
};

Example

sampleSize([1, 2, 3], 2); // [3,1]
sampleSize([1, 2, 3], 4); // [2,3,1]

Has the same functionality as `Array.prototype.prototype.splice()`, but returning a new array instead of mutating the original array.

Use Array.prototype.slice() and Array.prototype.concat() to get a new array with the new contents after removing existing elements and/or adding new elements. Omit the second argument, index, to start at 0. Omit the third argument, delCount, to remove 0 elements. Omit the fourth argument, elements, in order to not add any new elements.

Code

const shank = (arr, index = 0, delCount = 0, ...elements) =>
 arr
   .slice(0, index)
   .concat(elements)
   .concat(arr.slice(index + delCount));

Example

const names = ['alpha', 'bravo', 'charlie'];
const namesAndDelta = shank(names, 1, 0, 'delta'); // [ 'alpha', 'delta', 'bravo', 'charlie' ]
const namesNoBravo = shank(names, 1, 1); // [ 'alpha', 'charlie' ]
console.log(names); // ['alpha', 'bravo', 'charlie']

Randomizes the order of the values of an array, returning a new array.

Uses the Fisher-Yates algorithm to reorder the elements of the array.

Code

const shuffle = ([...arr]) => {
 let m = arr.length;
 while (m) {
   const i = Math.floor(Math.random() * m--);
   [arr[m], arr[i]] = [arr[i], arr[m]];
 }
 return arr;
};

Example

const foo = [1, 2, 3];
shuffle(foo); // [2, 3, 1], foo = [1, 2, 3]

Returns an array of elements that appear in both arrays.

Use Array.prototype.filter() to remove values that are not part of values, determined using Array.prototype.includes().

Code

const similarity = (arr, values) => arr.filter(v => values.includes(v));

Example

similarity([1, 2, 3], [1, 2, 4]); // [1, 2]

Returns the lowest index at which value should be inserted into array in order to maintain its sort order.

Check if the array is sorted in descending order (loosely). Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted.

Code

const sortedIndex = (arr, n) => {
 const isDescending = arr[0] > arr[arr.length - 1];
 const index = arr.findIndex(el => (isDescending ? n >= el : n <= el));
 return index === -1 ? arr.length : index;
};

Example

sortedIndex([5, 3, 2, 1], 4); // 1
sortedIndex([30, 50], 40); // 1

Returns the lowest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.

Check if the array is sorted in descending order (loosely). Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted, based on the iterator function fn.

Code

const sortedIndexBy = (arr, n, fn) => {
 const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
 const val = fn(n);
 const index = arr.findIndex(el => (isDescending ? val >= fn(el) : val <= fn(el)));
 return index === -1 ? arr.length : index;
};

Example

sortedIndexBy([{ x: 4 }, { x: 5 }], { x: 4 }, o => o.x); // 0

Returns the highest index at which value should be inserted into array in order to maintain its sort order.

Check if the array is sorted in descending order (loosely). Use Array.prototype.reverse() and Array.prototype.findIndex() to find the appropriate last index where the element should be inserted.

Code

const sortedLastIndex = (arr, n) => {
 const isDescending = arr[0] > arr[arr.length - 1];
 const index = arr.reverse().findIndex(el => (isDescending ? n <= el : n >= el));
 return index === -1 ? 0 : arr.length - index;
};

Example

sortedLastIndex([10, 20, 30, 30, 40], 30); // 4

Returns the highest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.

Check if the array is sorted in descending order (loosely). Use Array.prototype.map() to apply the iterator function to all elements of the array. Use Array.prototype.reverse() and Array.prototype.findIndex() to find the appropriate last index where the element should be inserted, based on the provided iterator function.

Code

const sortedLastIndexBy = (arr, n, fn) => {
 const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
 const val = fn(n);
 const index = arr
   .map(fn)
   .reverse()
   .findIndex(el => (isDescending ? val <= el : val >= el));
 return index === -1 ? 0 : arr.length - index;
};

Example

sortedLastIndexBy([{ x: 4 }, { x: 5 }], { x: 4 }, o => o.x); // 1

Performs stable sorting of an array, preserving the initial indexes of items when their values are the same.

Does not mutate the original array, but returns a new array instead.

Use Array.prototype.map() to pair each element of the input array with its corresponding index. Use Array.prototype.sort() and a compare function to sort the list, preserving their initial order if the items compared are equal. Use Array.prototype.map() to convert back to the initial array items.

Code

const stableSort = (arr, compare) =>
 arr
   .map((item, index) => ({ item, index }))
   .sort((a, b) => compare(a.item, b.item) || a.index - b.index)
   .map(({ item }) => item);

Example

const arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const stable = stableSort(arr, () => 0); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Returns the symmetric difference between two arrays, without filtering out duplicate values.

Create a Set from each array, then use Array.prototype.filter() on each of them to only keep values not contained in the other.

Code

const symmetricDifference = (a, b) => {
 const sA = new Set(a),
   sB = new Set(b);
 return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))];
};

Example

symmetricDifference([1, 2, 3], [1, 2, 4]); // [3, 4]
symmetricDifference([1, 2, 2], [1, 3, 1]); // [2, 2, 3]

Returns the symmetric difference between two arrays, after applying the provided function to each array element of both.

Create a Set by applying fn to each array's elements, then use Array.prototype.filter() on each of them to only keep values not contained in the other.

Code

const symmetricDifferenceBy = (a, b, fn) => {
 const sA = new Set(a.map(v => fn(v))),
   sB = new Set(b.map(v => fn(v)));
 return [...a.filter(x => !sB.has(fn(x))), ...b.filter(x => !sA.has(fn(x)))];
};

Example

symmetricDifferenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [ 1.2, 3.4 ]

Returns the symmetric difference between two arrays, using a provided function as a comparator.

Use Array.prototype.filter() and Array.prototype.findIndex() to find the appropriate values.

Code

const symmetricDifferenceWith = (arr, val, comp) => [
 ...arr.filter(a => val.findIndex(b => comp(a, b)) === -1),
 ...val.filter(a => arr.findIndex(b => comp(a, b)) === -1)
];

Example

symmetricDifferenceWith(
 [1, 1.2, 1.5, 3, 0],
 [1.9, 3, 0, 3.9],
 (a, b) => Math.round(a) === Math.round(b)
); // [1, 1.2, 3.9]

Returns all elements in an array except for the first one.

Return Array.prototype.slice(1) if the array's length is more than 1, otherwise, return the whole array.

Code

const tail = arr => (arr.length > 1 ? arr.slice(1) : arr);

Example

tail([1, 2, 3]); // [2,3]
tail([1]); // [1]

Returns an array with n elements removed from the beginning.

Use Array.prototype.slice() to create a slice of the array with n elements taken from the beginning.

Code

const take = (arr, n = 1) => arr.slice(0, n);

Example

take([1, 2, 3], 5); // [1, 2, 3]
take([1, 2, 3], 0); // []

Returns an array with n elements removed from the end.

Use Array.prototype.slice() to create a slice of the array with n elements taken from the end.

Code

const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);

Example

takeRight([1, 2, 3], 2); // [ 2, 3 ]
takeRight([1, 2, 3]); // [3]

Removes elements from the end of an array until the passed function returns `true`. Returns the removed elements.

Loop through the array, using a Array.prototype.reduceRight() and accumulating elements while the function returns falsy value.

Code

const takeRightWhile = (arr, func) =>
 arr.reduceRight((acc, el) => (func(el) ? acc : [el, ...acc]), []);

Example

takeRightWhile([1, 2, 3, 4], n => n < 3); // [3, 4]

Removes elements in an array until the passed function returns `true`. Returns the removed elements.

Loop through the array, using a for...of loop over Array.prototype.entries() until the returned value from the function is true. Return the removed elements, using Array.prototype.slice().

Code

const takeWhile = (arr, func) => {
 for (const [i, val] of arr.entries()) if (func(val)) return arr.slice(0, i);
 return arr;
};

Example

takeWhile([1, 2, 3, 4], n => n >= 3); // [1, 2]

Reduces a given Array-like into a value hash (keyed data store).

Given an Iterable or Array-like structure, call Array.prototype.prototype.reduce.call() on the provided object to step over it and return an Object, keyed by the reference value.

Code

const toHash = (object, key) =>
 Array.prototype.reduce.call(
   object,
   (acc, data, index) => ((acc[!key ? index : data[key]] = data), acc),
   {}
 );

Example

toHash([4, 3, 2, 1]); // { 0: 4, 1: 3, 2: 2, 1: 1 }
toHash([{ a: 'label' }], 'a'); // { label: { a: 'label' } }
// A more in depth example:
let users = [{ id: 1, first: 'Jon' }, { id: 2, first: 'Joe' }, { id: 3, first: 'Moe' }];
let managers = [{ manager: 1, employees: [2, 3] }];
// We use function here because we want a bindable reference, but a closure referencing the hash would work, too.
managers.forEach(
 manager =>
   (manager.employees = manager.employees.map(function(id) {
     return this[id];
   }, toHash(users, 'id')))
);
managers; // [ { manager:1, employees: [ { id: 2, first: "Joe" }, { id: 3, first: "Moe" } ] } ]

Returns every element that exists in any of the two arrays once.

Create a Set with all values of a and b and convert to an array.

Code

const union = (a, b) => Array.from(new Set([...a, ...b]));

Example

union([1, 2, 3], [4, 3, 2]); // [1,2,3,4]

Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.

Create a Set by applying all fn to all values of a. Create a Set from a and all elements in b whose value, after applying fn does not match a value in the previously created set. Return the last set converted to an array.

Code

const unionBy = (a, b, fn) => {
 const s = new Set(a.map(v => fn(v)));
 return Array.from(new Set([...a, ...b.filter(x => !s.has(fn(x)))]));
};

Example

unionBy([2.1], [1.2, 2.3], Math.floor); // [2.1, 1.2]

Returns every element that exists in any of the two arrays once, using a provided comparator function.

Create a Set with all values of a and values in b for which the comparator finds no matches in a, using Array.prototype.findIndex().

Code

const unionWith = (a, b, comp) =>
 Array.from(new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)]));

Example

unionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2, 1.5, 3, 0, 3.9]

Returns all unique values of an array.

Use ES6 Set and the ...rest operator to discard all duplicated values.

Code

const uniqueElements = arr => [...new Set(arr)];

Example

uniqueElements([1, 2, 2, 3, 4, 4, 5]); // [1, 2, 3, 4, 5]

Returns all unique values of an array, based on a provided comparator function.

Use Array.prototype.reduce() and Array.prototype.some() for an array containing only the first unique occurence of each value, based on the comparator function, fn. The comparator function takes two arguments: the values of the two elements being compared.

Code

const uniqueElementsBy = (arr, fn) =>
 arr.reduce((acc, v) => {
   if (!acc.some(x => fn(v, x))) acc.push(v);
   return acc;
 }, []);

Example

uniqueElementsBy(
 [
   { id: 0, value: 'a' },
   { id: 1, value: 'b' },
   { id: 2, value: 'c' },
   { id: 1, value: 'd' },
   { id: 0, value: 'e' }
 ],
 (a, b) => a.id == b.id
); // [ { id: 0, value: 'a' }, { id: 1, value: 'b' }, { id: 2, value: 'c' } ]

Returns all unique values of an array, based on a provided comparator function.

Use Array.prototype.reduce() and Array.prototype.some() for an array containing only the last unique occurence of each value, based on the comparator function, fn. The comparator function takes two arguments: the values of the two elements being compared.

Code

const uniqueElementsByRight = (arr, fn) =>
 arr.reduceRight((acc, v) => {
   if (!acc.some(x => fn(v, x))) acc.push(v);
   return acc;
 }, []);

Example

uniqueElementsByRight(
 [
   { id: 0, value: 'a' },
   { id: 1, value: 'b' },
   { id: 2, value: 'c' },
   { id: 1, value: 'd' },
   { id: 0, value: 'e' }
 ],
 (a, b) => a.id == b.id
); // [ { id: 0, value: 'e' }, { id: 1, value: 'd' }, { id: 2, value: 'c' } ]

Returns the unique symmetric difference between two arrays, not containing duplicate values from either array.

Use Array.prototype.filter() and Array.prototype.includes() on each array to remove values contained in the other, then create a Set from the results, removing duplicate values.

Code

const uniqueSymmetricDifference = (a, b) => [
 ...new Set([...a.filter(v => !b.includes(v)), ...b.filter(v => !a.includes(v))])
];

Example

uniqueSymmetricDifference([1, 2, 3], [1, 2, 4]); // [3, 4]
uniqueSymmetricDifference([1, 2, 2], [1, 3, 1]); // [2, 3]

Creates an array of arrays, ungrouping the elements in an array produced by zip.

Code

const unzip = arr =>
 arr.reduce(
   (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),
   Array.from({
     length: Math.max(...arr.map(x => x.length))
   }).map(x => [])
 );

Example

unzip([['a', 1, true], ['b', 2, false]]); //[['a', 'b'], [1, 2], [true, false]]
unzip([['a', 1, true], ['b', 2]]); //[['a', 'b'], [1, 2], [true]]

Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function.

Use Math.max.apply() to get the longest subarray in the array, Array.prototype.map() to make each element an array. Use Array.prototype.reduce() and Array.prototype.forEach() to map grouped values to individual arrays. Use Array.prototype.map() and the spread operator (...) to apply fn to each individual group of elements.

Code

const unzipWith = (arr, fn) =>
 arr
   .reduce(
     (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),
     Array.from({
       length: Math.max(...arr.map(x => x.length))
     }).map(x => [])
   )
   .map(val => fn(...val));

Example

unzipWith([[1, 10, 100], [2, 20, 200]], (...args) => args.reduce((acc, v) => acc + v, 0)); // [3, 30, 300]

Filters out the elements of an array, that have one of the specified values.

Use Array.prototype.filter() to create an array excluding(using !Array.includes()) all given values.

(For a snippet that mutates the original array see pull)

Code

const without = (arr, ...args) => arr.filter(v => !args.includes(v));

Example

without([2, 1, 2, 3], 1, 2); // [3]

Creates a new array out of the two supplied by creating each possible pair from the arrays.

Use Array.prototype.reduce(), Array.prototype.map() and Array.prototype.concat() to produce every possible pair from the elements of the two arrays and save them in an array.

Code

const xProd = (a, b) => a.reduce((acc, x) => acc.concat(b.map(y => [x, y])), []);

Example

xProd([1, 2], ['a', 'b']); // [[1, 'a'], [1, 'b'], [2, 'a'], [2, 'b']]

Creates an array of elements, grouped based on the position in the original arrays.

Use Math.max.apply() to get the longest array in the arguments. Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements. If lengths of the argument-arrays vary, undefined is used where no value could be found.

Code

const zip = (...arrays) => {
 const maxLength = Math.max(...arrays.map(x => x.length));
 return Array.from({ length: maxLength }).map((_, i) => {
   return Array.from({ length: arrays.length }, (_, k) => arrays[k][i]);
 });
};

Example

zip(['a', 'b'], [1, 2], [true, false]); // [['a', 1, true], ['b', 2, false]]
zip(['a'], [1, 2], [true, false]); // [['a', 1, true], [undefined, 2, false]]

Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.

Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.prototype.reduce().

Code

const zipObject = (props, values) =>
 props.reduce((obj, prop, index) => ((obj[prop] = values[index]), obj), {});

Example

zipObject(['a', 'b', 'c'], [1, 2]); // {a: 1, b: 2, c: undefined}
zipObject(['a', 'b'], [1, 2, 3]); // {a: 1, b: 2}

Creates an array of elements, grouped based on the position in the original arrays and using function as the last value to specify how grouped values should be combined.

Check if the last argument provided is a function. Use Math.max() to get the longest array in the arguments. Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements. If lengths of the argument-arrays vary, undefined is used where no value could be found. The function is invoked with the elements of each group (...group).

Code

const zipWith = (...array) => {
 const fn = typeof array[array.length - 1] === 'function' ? array.pop() : undefined;
 return Array.from(
   { length: Math.max(...array.map(a => a.length)) },
   (_, i) => (fn ? fn(...array.map(a => a[i])) : array.map(a => a[i]))
 );
};

Example

zipWith([1, 2], [10, 20], [100, 200], (a, b, c) => a + b + c); // [111,222]
zipWith(
 [1, 2, 3],
 [10, 20],
 [100, 200],
 (a, b, c) => (a != null ? a : 'a') + (b != null ? b : 'b') + (c != null ? c : 'c')
); // [111, 222, '3bc']

agrublev/array.md

Returns true if the provided predicate function returns true for all elements in a collection, false otherwise.

Code

Example

Check if all elements in an array are equal.

Code

Example

Returns true if the provided predicate function returns true for at least one element in a collection, false otherwise.

Code

Example

Converts a 2D array to a comma-separated values (CSV) string.

Code

Example

Splits values into two groups. If an element in filter is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.

Code

Example

Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If the predicate function returns a truthy value, the collection element belongs to the first group; otherwise, it belongs to the second group.

Code

Example

Chunks an array into smaller arrays of a specified size.

Code

Example

Removes falsey values from an array.

Code

Example

Groups the elements of an array based on the given function and returns the count of elements in each group.

Code

Example

Counts the occurrences of a value in an array.

Code

Example

Deep flattens an array.

Code

Example

Returns the difference between two arrays.

Code

Example

Returns the difference between two arrays, after applying the provided function to each array element of both.

Code

Example

Filters out all values from an array for which the comparator function does not return true.

Code

Example

Returns a new array with n elements removed from the left.

Code

Example

Returns a new array with n elements removed from the right.

Code

Example

Removes elements from the end of an array until the passed function returns true. Returns the remaining elements in the array.

Code

Example

Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.

Code

Example

Returns every nth element in an array.

Code

Example

Filters out the non-unique values in an array.

Code

Example

Filters out the non-unique values in an array, based on a provided comparator function.

Code

Example

Returns the last element for which the provided function returns a truthy value.

Code

Example

Returns the index of the last element for which the provided function returns a truthy value.

Code

Example

Flattens an array up to the specified depth.

Code

Example

Executes a provided function once for each array element, starting from the array's last element.

Code

Example

Groups the elements of an array based on the given function.

Code

Example

Returns the head of a list.

Returns `true` if the provided predicate function returns `true` for all elements in a collection, `false` otherwise.

Returns `true` if the provided predicate function returns `true` for at least one element in a collection, `false` otherwise.

Splits values into two groups. If an element in `filter` is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.

Filters out all values from an array for which the comparator function does not return `true`.

Returns a new array with `n` elements removed from the left.

Returns a new array with `n` elements removed from the right.

Removes elements from the end of an array until the passed function returns `true`. Returns the remaining elements in the array.

Removes elements in an array until the passed function returns `true`. Returns the remaining elements in the array.

Returns all indices of `val` in an array.

Initializes an array containing the numbers in the specified range where `start` and `end` are inclusive with their common difference `step`.

Initializes an array containing the numbers in the specified range (in reverse) where `start` and `end` are inclusive with their common difference `step`.

Returns `1` if the array is sorted in ascending order, `-1` if it is sorted in descending order or `0` if it is not sorted.

Converts an array of objects to a comma-separated values (CSV) string that contains only the `columns` specified.

Takes any number of iterable objects or objects with a `length` property and returns the longest one.

Returns the `n` maximum elements from the provided array.

Returns the `n` minimum elements from the provided array.

Returns `true` if the provided predicate function returns `false` for all elements in a collection, `false` otherwise.