Function that returns difference of two arrays of strings in javascript

Question

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What is the fastest or most elegant way to compute a set difference using Javascript arrays?

I need help with devising a function that will return the difference between two arrays of strings in Javascript (jQuery is acceptable as well).

I am basically looking for a function that calculates array A minus B.

So if we have the followin"

A = ['Istanbul', 'Hong Kong', 'Berlin'];
B = ['Berlin', 'Bonn'];

Calling diff = minus(A,B) should result with diff being populated with the following values ['Istanbul', 'Hong Kong']

I do not want to use an additional library like JS Set.

Please help with suggestions ...

Have you made any attempts to solve this already? If you have, what went wrong, what would you like us to help with? A part of the problem, or the whole of the problem? — David Thomas, Jul 28 '12 at 20:45

score 22 · Accepted Answer · answered Jul 28 '12 at 20:48

22

function diff(A, B) {
    return A.filter(function (a) {
        return B.indexOf(a) == -1;
    });
}

answered Jul 28 '12 at 20:48

Casey Chu

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adeneo · Answer 2 · 2017-11-08T19:17:12.313

The fastest would probably be a regular loop

var A = ['Istanbul', 'Hong Kong', 'Berlin'],
    B = ['Berlin', 'Bonn'],
    C = [];

for (var i=A.length; i--;) {
   if (B.indexOf(A[i]) === -1) 
       C.push(A[i]);
}

console.log(C);

The most elegant is opinion-based, but something like

var A = ['Istanbul', 'Hong Kong', 'Berlin'],
    B = ['Berlin', 'Bonn'];

var C = A.filter(x => !B.includes(x));

console.log(C);

score 3 · Answer 3 · answered Jul 28 '12 at 20:49

3

Here:

var minus = function ( a, b ) {
    return a.filter(function ( name ) {
        return b.indexOf( name ) === -1;
    });
};

Live demo: http://jsfiddle.net/SjF9p/

answered Jul 28 '12 at 20:49

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Function that returns difference of two arrays of strings in javascript

3 Answers3