Javascript Equivalent to C# LINQ Select

Question

Following this question here :

Using the checked binding in knockout with a list of checkboxes checks all the checkboxes

I've created some checkboxes using knockout that allow selection from an array. working fiddle taken from above post:

http://jsfiddle.net/NsCXJ/

Is there a simple way of creating an array of just the fruit's ID's?

I'm more at home with C# where I would do something along the lines of selectedFruits.select(fruit=>fruit.id);

Is there some method/ready made function for doing something similar with javascript/jquery? Or would the simplest option be to loop through the list and create a second array? I intend to post the array back to the server in JSON so am trying to minimize the data sent.

Answer 1

Take a peek at underscore.js which provides many linq like functions. In the example you give you would use the map function.

Answer 2

I have build a Linq library for TypeScript under TsLinq.codeplex.com that you can use for plain javascript too. That library is 2-3 times faster than Linq.js and contains unit tests for all Linq methods. Maybe you could review that one.

Answer 3

I know it is a late answer but it was useful to me! Just to complete, using the $.grep function you can emulate the linq where().

Linq:

var maleNames = people
.Where(p => p.Sex == "M")
.Select(p => p.Name)

Javascript:

// replace where  with $.grep
//         select with $.map
var maleNames = $.grep(people, function (p) { return p.Sex == 'M'; })
            .map(function (p) { return p.Name; });

Answer 4

Since you're using knockout, you should consider using the knockout utility function arrayMap() and it's other array utility functions.

Here's a listing of array utility functions and their equivalent LINQ methods:

arrayFilter() -> Where()
arrayFirst() -> First()
arrayForEach() -> (no direct equivalent)
arrayGetDistictValues() -> Distinct()
arrayIndexOf() -> IndexOf()
arrayMap() -> Select()
arrayPushAll() -> (no direct equivalent)
arrayRemoveItem() -> (no direct equivalent)
compareArrays() -> (no direct equivalent)

So what you could do in your example is this:

var mapped = ko.utils.arrayMap(selectedFruits, function (fruit) {
    return fruit.id;
});

If you want a LINQ like interface in javascript, you could use a library such as linq.js which offers a nice interface to many of the LINQ methods.

var mapped = Enumerable.From(selectedFruits)
    .Select("$.id") // 1 of 3 different ways to specify a selector function
    .ToArray();

Answer 5

The ES6 way:

let people = [{firstName:'Alice',lastName:'Cooper'},{firstName:'Bob',age:'Dylan'}];
let names = Array.from(people, p => p.firstName);
for (let name of names) {
  console.log(name);
}

also at: https://jsfiddle.net/52dpucey/

Answer 6

You can also try linq.js

In linq.js your

selectedFruits.select(fruit=>fruit.id);

will be

Enumerable.From(selectedFruits).Select(function (fruit) { return fruit.id;  });