JavaScript equivalents of some common C# LINQ methods. To help me remember!

JS-LINQ.js

// JS array equivalents to C# LINQ methods - by Dan B.

// First: This version using older JavaScript notation for universal browser support (scroll down for ES6 version):

// Here's a simple array of "person" objects
var people = [ 
	{ name: "John", age: 20 }, 
	{ name: "Mary", age: 35 }, 
	{ name: "Arthur", age: 78 }, 
	{ name: "Mike", age: 27 }, 
	{ name: "Judy", age: 42 }, 
	{ name: "Tim", age: 8 } 
];

// filter is equivalent to Where

var youngsters = people.filter(function (item) {
	return item.age < 30;
});

console.log("People younger than 30:", youngsters);


// map is equivalent to Select

var names = people.map(function (item) {
	return item.name;
});

console.log("Just the names of people:", names);


// every is equivalent to All

var allUnder40 = people.every(function (item) {
	return  item.age < 40;
});

console.log("Are all people under 40?", allUnder40); // false


// some is equivalent to Any

var anyUnder30 = people.some(function (item) {
	return  item.age < 30;
});

console.log("Are any people under 30?", anyUnder30); // true


// reduce is "kinda" equivalent to Aggregate (and also can be used to Sum)

var aggregate = people.reduce(function (item1, item2) {
	return  { name: '', age: item1.age + item2.age };
});

console.log("Aggregate age", aggregate.age);  // { age: 210 }


// sort is "kinda" like OrderBy (but it sorts the array in place - eek!)

var orderedByName = people.sort(function (a, b) {
	return  a.name < b.name ? 1 : -1;
})

console.log("Ordered by name:", orderedByName); 


// and, of course, you can chain function calls 

var namesOfPeopleOver30OrderedDesc = people.filter(function (person) {
	return person.age > 30;
}).
map(function (person) {
	return person.name;
}).
sort(function (a, b) {
	return a > b ? 1 : -1;
});

console.log("And now.. the names of all people over 30 ordered by name descending:", namesOfPeopleOver30OrderedDesc);



// Second: And now the more modern ES6 way of doing this using arrow functions (lambdas!)...

const peoples = [ 
	{ name: "John", age: 20 }, 
	{ name: "Mary", age: 35 }, 
	{ name: "Arthur", age: 78 }, 
	{ name: "Mike", age: 27 }, 
	{ name: "Judy", age: 42 }, 
	{ name: "Tim", age: 8 } 
];

// filter is equivalent to Where

const youngPeople = peoples.filter(p => p.age < 30);

console.log("People younger than 30:", youngPeople);


// map is equivalent to Select

const justNames = peoples.map(p => p.name);

console.log("Just the names of people:", justNames);

// every is equivalent to All

const peopleUnder40 = peoples.every(p => p.age < 40);

console.log("Are all people under 40?", peopleUnder40); // false


// some is equivalent to Any

const areAnyUnder30 = peoples.some(p => p.age < 30);

console.log("Are any people under 30?", areAnyUnder30); // true


// reduce is "kinda" equivalent to Aggregate (and also can be used to Sum)

const aggregatedAge = peoples.reduce((p1, p2) => {
	return  { name: '', age: p1.age + p2.age }
});

console.log("Aggregate age:", aggregatedAge.age);  // { age: 210 }


// sort is "kinda" like OrderBy (but it sorts the array in place - eek!)

const peopleOrderedByName = peoples.sort((p1, p2) => p1.name < p2.name ? 1 : -1);

console.log("Ordered by name:", peopleOrderedByName); 


// and, of course, you can chain function calls 

const peepsOver30OrderedDesc = peoples.filter(p => p.age > 30).map(p => p.name).sort((p1, p2) => p1 > p2 ? 1 : -1);

console.log("Chained", peepsOver30OrderedDesc);

The Array functions in Javascript are similar in result, but not in implementation with C# LINQ. If you have an array with a million rows and you filter it, then map it, then get the first item, you get an array at each step: a million filterings and a thousand item array, a thousand mappings in another thousand item array. all for one item. I've researched a LINQ like approach in Javascript here: https://siderite.dev/blog/linq-in-javascript-linqer/

Thanks!!!

Thanks, you may want to update the order by stuff - https://gist.github.com/amul047/5fa79670adcc8693269c066096019a0f/revisions

@amul047 Thanks, have done!

You deserve a medal

Nice overview, thank you very much. For someone coming from C# this is very helpful.

But it has only one problem, a huge problem. LINQ is totally lazy, but JS function isn't.

@axispod check out iterable-query - Query API for JavaScript Iterables and Async Iterables, I think it's very close to C# lazy LINQ.

Thanks so much ❤

nice

Thank you!

Thank you :D

// sort is "kinda" like OrderBy (but it sorts the array in place - eek!)

var orderedByName = people.sort(function (a, b) {
	return  a.name > b.name ? 1 : -1;
})

console.log("Ordered by name"); 

console.log(orderedByName);

You can use this if you want to sort in a new array without change the original array (not in place):

var orderedByName = people.slice().sort(function (a, b) {
	return  a.name > b.name ? 1 : -1;
})

console.log("Ordered by name"); 
console.log(orderedByName);

console.log("Original array"); 
console.log(people);

Good shout @Serrin

Thanks bro

Thanks a ton 👍

It can also be written using arrow functions:

  const youngsters = people.filter(item => item.age < 30);
  const allUnder40 = people.every(item => item.age < 40); 
  const orderedByName = people.sort((a, b) => a.name > b.name ? 1 : -1);

@SergeyDorofeev Yeah, I keep meaning to update it with arrow functions, but they weren't widely available when I first wrote this!

Nice

Thanks so much!!

This is beautiful! ❤️

https://brunoscopelliti.com/blog/csharp-linq-equivalents-of-javascript-array-methods/

Omo!!! This is quality.

great

@tyler-kearney

I dont think filter is a good way to represent FirstOrDefault. It functions the same but one of the primary benefits of FirstOrDefault is that it stops early. Filter has to parse the entire list before anything can be returned.

I agree. I use find as an equivalent to FirstOrDefault.

const firstYoungster = peoples.find(p => p.age < 30);

@tyler-kearney
I dont think filter is a good way to represent FirstOrDefault. It functions the same but one of the primary benefits of FirstOrDefault is that it stops early. Filter has to parse the entire list before anything can be returned.

I agree. I use find as an equivalent to FirstOrDefault.

const firstYoungster = peoples.find(p => p.age < 30);

Hi. Yes. I agree now. Back in 2017 find was still quite new. Especially for production code.

Edit: and I'll admit, I was unaware of find at the time

@tyler-kearney

I dont think filter is a good way to represent FirstOrDefault. It functions the same but one of the primary benefits of FirstOrDefault is that it stops early. Filter has to parse the entire list before anything can be returned.

const firstOrDefault =[].at(0) || defaultValue 
const lastOrDefault =[].at(-1) || defaultValue 

Thanks so much!! You're are a life saver!

flatMap is like SelectMany

let items = [
  { text: "a", stuff: [ 1, 2, 3] },
  { text: "b", stuff: [ 4, 5 ] },
  { text: "c", stuff: [ 6, 7, 8] },
  { text: "d", stuff: [ 9, 0] }
];

flatStuff() {
    return items.flatMap(m => m.stuff)
}

console.log(flatStuff())

returns

[1,2,3,4,5,6,7,8,9,0]

JSFiddle

So helpful, thanks!