Filter one array of elements using another array

Question

I'm a bit more familiar with python, so what is the javascript equivalent of:

In [25]: listA = [1,2,3,4,5,1,1]
In [26]: listB = [1,2]
In [27]: intersect = [element for element in listA if element in listB]
In [28]: intersect

Out[28]: [1, 2, 1, 1]

This is the closest I can get:

var arrA = [1,1,3,4,5,5,6];
var arrB = [1,5];
var arrC = [];
$.each(arrA, function(i,d){ if (arrB.indexOf(d)> -1){arrC.push(d);} ;});

Any comments on preferred methods? I saw this answer, but it was not exactly what I wanted to answer.

I'm new to javascript, just thought I'd see what people have to say. — gus
– gus, Commented Mar 11, 2013 at 7:35
If it works and you want to know whether there's something better, you're better off at codereview.stackexchange.com. Also, this isn't "pure" JavaScript ($.each is from the jQuery library). If you're new to JavaScript don't use jQuery at first. First get used to the language and see what isn't possible in JavaScript, then start to use a library to get rid of the limitations. — Zeta
– Zeta, Commented Mar 11, 2013 at 7:39

KooiInc · Accepted Answer · 2013-03-11 08:06:23Z

8

You could use Array.filter like this:

var aa = [1,2,3,4,5,1,1]
   ,ab = [1,2]
   ,ac = aa.filter(function(a){return ~this.indexOf(a);},ab);
//=> ac is now [1,2,1,1]

Or as extension for Array.prototype

Array.prototype.intersect = function(arr){
 return this.filter(function(a){return ~this.indexOf(a);},arr);
}
// usage
[1,2,3,4,5,1,1].intersect([1,2]); //=> [1,2,1,1]

See MDN for the Array.filter method (also contains a shim for older browsers)

edited Mar 11, 2013 at 8:06

answered Mar 11, 2013 at 7:56

KooiInc

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2 Comments

S Panfilov Over a year ago

I didn't catch what ~ do here before this.indexOf?

KooiInc Over a year ago

It's a bit of a trick using the bitwise NOT operator: if indexOf == -1 (nothing found), applying the ~-operator makes it 0 and in javascript 0 is falsy . So ~this.indexOf(a) is shorthand for this.indexOf(a) !== -1. See also: developer.mozilla.org/en/docs/Web/JavaScript/Reference/…

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