Re: Difference between two arrays

From	Denis McMahon <denismfmcmahon@gmail.com>
Newsgroups	comp.lang.javascript
Subject	Re: Difference between two arrays
Date	2014-05-27 05:58 +0000
Organization	A noiseless patient Spider
Message-ID	<lm19ir$kag$5@dont-email.me> (permalink)
References	<z_ydnZKbtslwbR7OnZ2dnUVZ_rGdnZ2d@westnet.com.au>

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On Tue, 27 May 2014 11:55:03 +1000, Andrew Poulos wrote:

> If I have two "simple" arrays and I need to create a third array of
> elements that are only in one of the arrays. I found this
> 
> Array.prototype.difference = function (a) {
>    return this.filter(function (i) {
>      return !(a.indexOf(i) > -1);
>    });
> };
> 
> which I don't fully understand but the issue with it that I have is that
> I need to run it on both arrays to get all the differences. For example

It's not finding the differences between two arrays, it's finding the 
elements of one array which are not in the other array.

Think of it like an array subtraction:

arr1 = [ a, b, c, d, e ]
arr2 = [ b, c, d, e, f ]

arr1 - arr2 = those elements of arr1 that are not in arr2 = [ a ]
arr2 - arr1 = those elements of arr2 that are not in arr1 = [ f ]

( arr1 - arr2 ) + ( arr2 - arr1 ) 

In terms of set theory, you're taking the union of the set differences to 
create the symmetric difference.

-- 
Denis McMahon, denismfmcmahon@gmail.com

Thread

Difference between two arrays Andrew Poulos <ap_prog@hotmail.com> - 2014-05-27 11:55 +1000
  Re: Difference between two arrays Denis McMahon <denismfmcmahon@gmail.com> - 2014-05-27 05:58 +0000
  Re: Difference between two arrays John C <rescattered@gmail.com> - 2014-05-27 03:34 -0700
    Re: Difference between two arrays Spamless <Spamless@Nil.nil> - 2014-05-31 06:35 -0500
      Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-05-31 14:57 +0200
        Re: Difference between two arrays Spamless <Spamless@Nil.nil> - 2014-06-01 03:43 -0500
          Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-06-01 14:01 +0200
            Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-06-01 16:53 +0200
  Re: Difference between two arrays Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-05-27 13:41 +0100
    Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-05-27 17:41 +0200
    Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-05-27 17:49 +0200
      Re: Difference between two arrays Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-05-27 17:34 +0100
        Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-05-27 19:33 +0200
          Re: Difference between two arrays Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-05-27 20:03 +0100
    Re: Difference between two arrays Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-05-27 17:16 +0100
      Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-05-27 19:29 +0200
  Re: Difference between two arrays Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-05-27 17:21 +0200
  Re: Difference between two arrays Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-05-28 18:22 +0100
    Re: Difference between two arrays Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-05-30 22:23 +0100
    Re: Difference between two arrays "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2014-05-31 14:59 -0700
      Re: Difference between two arrays "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-06-01 00:50 +0200
        Re: Difference between two arrays "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2014-05-31 16:17 -0700
          Re: Difference between two arrays "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-06-01 10:49 +0200
            Re: Difference between two arrays "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2014-06-01 13:37 -0700
      Re: Difference between two arrays Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-06-01 18:56 +0100

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