Sorting alphanumeric array with java-script

Question

I have a alphanumeric array -

var a1 =["3800tl-24G-2XG-PoEP", "3500", "stack-TA", "2620-48-PoEP", "2120", "3800tl-24G-2XG-PoEP"];

I tried sorting this array using natsort which gives me the correct output -

`Array ( [4] => 2120 [3] => 2620-48-PoEP [1] => 3500 [0] => 3800tl-24G-2XG-PoEP [5] => 3800tl-24G-2XG-PoEP [2] => stack-TA )`

I tried doing the same with javascript -

var a1 =["3800tl-24G-2XG-PoEP", "3500", "stack-TA", "2620-48-PoEP", "2120", "3800tl-24G-2XG-PoEP"];

    var a2 = a1.sort(function(a,b){
        var charPart = [a.substring(0,1), b.substring(0,1)],
            numPart = [a.substring(1)*1, b.substring(1)*1];

        if(charPart[0] < charPart[1]) return -1;
        else if(charPart[0] > charPart[1]) return 1;
        else{ //(charPart[0] == charPart[1]){
            if(numPart[0] < numPart[1]) return -1;
            else if(numPart[0] > numPart[1]) return 1;
            return 0;
        }
    });
    $('#r').html(a2.toString())

which gives me the output - 2620-48-PoEP,2120,3800tl-24G-2XG-PoEP,3500,3800tl-24G-2XG-PoEP,stack-TA.

Why the javascript code is not taking 2120 as the 1st element. What is wrong with the javascript code ?

It'll not help you to resolve your problem, but when you try to get a char would be easier to use brackets [], instead of substring(), e.g.: var charPart = [a[0], b[0]]; — Givi
– Givi, Commented Apr 4, 2014 at 9:32

raina77ow · Accepted Answer · 2014-04-04 09:28:42Z

1

Replace this line...

[a.substring(1)*1, b.substring(1)*1]

... with ...

[parseInt(a.substring(1), 10), parseInt(b.substring(1), 10)]

... and it will work (demo), though the sorting function still won't be as universal as possible.

Explanation: a.substr(1)*1 (better written as just +a.substr(1), btw) casts that substring into Number type. In theory, that should give you a real number. In JS practice, however, it'll fail (giving NaN) if the rest of the string is not a complete representation of a number, having nothing except but that number.

For example, for 2620-48-PoEP line, '620-48-PoEP' is cast to Number. Now JS cannot interpret it as 620 - it'll be too bold for it, as there are some other meaningful (=non-whitespace) characters there. So instead of giving you 620, it gives you NaN.

Now, any comparison between NaN and NaN is false (expect !=) - and that'll essentially make your sorting function gone haywire.

As a sidenote, array.sort updates the object in-place - you don't need to use another reference to it (a2 variable), you can work with a1.

edited Apr 4, 2014 at 9:28

answered Apr 4, 2014 at 9:16

raina77ow

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5 Comments

user3496418 Over a year ago

after replacing its not returning anything

raina77ow Over a year ago

@user3496418 Check the demo (console output).

user3496418 Over a year ago

can you see the output ?

raina77ow Over a year ago

Sorry, not sure what do you mean. After a1.sort, you'll end up with that array sorted, so you can do whatever you want with it. For example, show in HTML with $('#r').html(a1.join('<br>'));, like in this demo.

user3496418 Over a year ago

Yea I understood that. thank you for such a detailed explanation.

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