Quick Coffee

In which we list tips, tricks, and reminders.

Misc.
Strings
Words
Arrays
Math
Mutator Methods
Iteration Methods
Prototype Extensions

Links to official docs:

Helper methods for testing and whatnot.

{print, ok, eq, arrayEq} = require 'tester'

Misc.

List method names of arrays and strings:

dir = (obj) -> Object.getOwnPropertyNames(obj.constructor.prototype)

print dir []    # last, extend, pop, push, ...
print dir 's'   # upper, length, lower, ...

A few numbers for stuff below.

nums = [1..4]

Print each value:

print x for x in nums                 # 1 2 3 4

Print index, value pairs:

print i, x for x, i in nums

Print key, value pairs of object:

numbers = 
  one: 1
  two: 2
  three: 3

print key, value for key, value of numbers

Filter out even values:

isEven = (x) -> x % 2 == 0
arrayEq [1, 3], 
        (x for x in nums when not isEven x)

Generate list of squares:

square = (x) -> Math.pow(x, 2)

arrayEq [1, 4, 9, 16], 
        nums.map square

Equivalent to ...

arrayEq [1, 4, 9, 16],
        (square x for x in nums)

Generate list of squares for values in object:

numbers = 
  one: 1
  two: 2
  three: 3

arrayEq [1, 4, 9], 
        (square x for word, x of numbers)

A simple counter:

class Counter
  constructor: (@total=0) ->
  inc: (n=1) -> @total += n

counter = (total=0) -> 
  (inc=1) -> total += inc

count = new Counter(5)
eq count.inc(), 6
eq count.inc(), 7
eq count.total, 7

Strings

Split a string:

words = "foo bar baz biz buz".split(" ")
arrayEq words, ['foo', 'bar', 'baz', 'biz', 'buz']

words = "foo|bar|baz|biz|buz".split("|")
arrayEq words, ['foo', 'bar', 'baz', 'biz', 'buz']

Extend prototype w/ pythonic method names

String::upper = -> @toUpperCase()
String::lower = -> @toLowerCase()
eq 'FOO', 'foo'.upper()
eq 'foo', 'FOO'.lower()

Words

wordlist = "foo bar baz biz buz".split(" ")
ok 'foo' in wordlist
ok not ('boo' in wordlist)

Make a dict (associative array) for easy lookups:

dict = {}
for word in wordlist
  dict[word] = 1

ok dict['foo'] and not dict['boo']
ok dict.foo and not dict.boo

Pass in a string of words for easy lookups:

makeDict = (wordlist) -> 
  new class then constructor: ->
    @[word] = 1 for word in wordlist.split(" ")

dict = makeDict "foo bar baz biz buz"
ok dict['foo'] and not dict['boo']
ok dict.foo and not dict.boo

Variant version:

class Dict
  constructor: (wordlist) ->
    @[word] = 1 for word in wordlist.split(" ")

dict = new Dict "foo bar baz biz buz"
ok dict['foo'] and not dict['boo']
ok dict.foo and not dict.boo

Filter out non-dict words:

sent = "I want to foo that bar with biz"
dictwords = (word for word in sent.split(" ") when dict[word])
arrayEq dictwords, ['foo', 'bar', 'biz']

Arrays

We'll use this list of numbers below.

nums = [1..4]

Get length of array:

eq 4, nums.length

Mutator Methods

Pop last element: x = nums.pop() arrayEq nums, [1..3]

Push element to end and return length:

n = nums.push(x)
arrayEq nums, [1..4]
eq nums.length, n

Reverse order:

arrayEq nums.reverse(), [4..1]

Sort elements:

arrayEq nums.sort(), [1..4]

Shift (pop off first element):

x = nums.shift()
arrayEq nums, [2..4]

Unshift (push element to front and return length):

n = nums.unshift(x)
arrayEq nums, [1..4]
eq n, 4

Lexicographic sort (default):

nums = [9, 10, 100, 20, 200, 3, 1]
arrayEq nums.sort(), [1, 10, 100, 20, 200, 3, 9]

Numeric sort:

numeric = (a, b) -> a - b
arrayEq nums.sort(numeric), [1, 3, 9, 10, 20, 100, 200]

Splice first element:

nums = [1..10]
x = nums.splice(0, 1)     # same as nums.pop()
arrayEq nums, [2..10]
arrayEq x, [1]

Splice first two elements:

nums = [1..10]
x = nums.splice(0, 2)
arrayEq nums, [3..10]
arrayEq x, [1, 2]

Splice out second element:

nums = [1..10]
x = nums.splice(1, 1)
expected = [1].concat [3..10]
arrayEq nums, expected
arrayEq x, [2]

Splice out second and third elements:

nums = [1..10]
arrayEq nums.splice(1, 2), [2, 3]
arrayEq nums, [1].concat [4..10]

Note the syntax: array.splice(index, count)

Splice in elements at start of array (index 0):

nums = [1..4]
nums.splice(0, 0, 'a', 'b')
arrayEq nums, ['a', 'b'].concat [1..4]

Replace two elements at start of array (index 0):

nums = [1..4]
nums.splice(0, 2, 'a', 'b')
arrayEq nums, ['a', 'b', 3, 4]

Note the syntax: array.splice(index, count, a, b, ...)

nums = [1..4]
nums.splice(0, 2, 'a', 'b', 'c')
arrayEq nums, ['a', 'b', 'c', 3, 4]

Concatenate:

arrayEq [1..10],
        [1..5].concat [6..10]

arrayEq [1..10],
        [1..5].concat 6, 7, 8, 9, 10

Join list elements into a string:

eq '1,2,3,4', [1..4].join()
eq '1|2|3|4', [1..4].join('|')
eq '1234', [1..4].join('')

Sum values in a list:

nums = [1..4]
eq 10, nums.reduce (x, y) -> x + y

Test for some true elements:

some = (list, fn) ->
  for e in list
    return yes if fn e
  no

gtThree = (x) -> x > 3
gtFour = (x) -> x > 4

ok some nums, gtThree
ok not some nums, gtFour

Test that all elements are true:

all = (list, fn) ->
  for e in list
    return no unless fn e
  yes

ltFive = (x) -> x < 5
  
ok not all nums, gtThree
ok not all nums, gtFour
ok all nums, ltFive

Prototype Extensions

It can be handy to define custom array methods on the Array prototype so they can be used like the reduce method above.

Sum array of numbers:

Array::sum = (x, y) -> @.reduce (x, y) -> x + y

eq 10, nums.sum()

Get the last item:

Array::last = -> @[@.length - 1]

eq 4, nums.last()

Trim out all falsy values from an array:

Array::compact = ->
  item for item in @ when item

arrayEq [1, 2, 3], 
        [1, false, 2, '', 3, null].compact()

Flatten a nested array:

Array::flatten = ->
  flat = []
  for e in @
    if Array.isArray e
      flat = flat.concat e.flatten()
    else
      flat.push e
  flat

arrayEq [1..4],
        [1, [2, [3, [4]]]].flatten()

Extend an array (as mutator method):

Array::extend = (other) -> 
  Array::push.apply @, other
  @

letters = ['a', 'b', 'c']
letters.extend ['d', 'e', 'f']
eq letters.length, 6
eq letters.last(), 'f'

Iteration Methods

Collect the doubled value for each number in nums:

nums = [1..4]
doubles = []
double = (x) -> doubles.push (x * 2)
nums.forEach double
arrayEq doubles, [2, 4, 6, 8]

Every element meets condition?

ok doubles.every (x) -> x > 1
ok not doubles.every (x) -> x < 4

Some elements meet condition?

ok doubles.some (x) -> x < 4
ok not doubles.some (x) -> x > 50

Filter out elements not meeting condition:

arrayEq [3, 4], nums.filter (x) -> x > 2

Map a function to each element:

arrayEq [2..5], nums.map (x) -> x + 1

Reduce elements to a single value:

eq 10, nums.reduce (x, y) -> x + y

Math

Find min/max in a list:

nums = [10, -10, 100, 0, 1]
eq 100, Math.max.apply @, nums
eq -10, Math.min.apply @, nums

Primality tester:

isPrime = (x) ->
  p = 2
  while p * p <= x
    return false if x % p == 0
    p += 1
  true

Find primes:

arrayEq [1, 2, 3, 5, 7, 11, 13, 17, 19],
        (x for x in [1..20] when isPrime x)

Find factors:

factors = (n) -> i for i in [1..n] when n % i == 0

arrayEq [1, 11], 
        factors 11

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