In multiple browsers, the following code doesn't sort the numbers correctly:
a = new Array();
a.push(10);
a.push(60);
a.push(20);
a.push(30);
a.push(100);
document.write(a.sort())
It returns 10,100,20,30,60.
Anyone know why?
5 Answers
a.sort(function(a,b){return a - b})
These can be confusing.... check this link out.
5 Comments
veich
In ES6 it's even more elegant:
a.sort((a, b) => a - b)
Rohith
quiet elegant. I used the ES6Version of the same and works like a charm, and why this is not the answer????
Joseph Marikle
@Rohith This answer was written when I had only just recently joined SO, and it's honestly not a very well written answer either. :P The solution is wonderful, but it doesn't explain why the issue occurs, so I think Jason's answer should definitely be the marked solution. I'm glad you found my answer useful, though!
unfollow
small note here -- generally speaking you never want to reuse variable names (even if they're block scoped). we're sorting an array called 'a' and then reusing 'a' to represent an array item. if this is confusing anyone 'a' is not the same value. to clarify:
array.sort((a, b) => a - b)
Stefnotch
That's wrong when the question is "how to sort numbers correctly". It doesn't take NaNs into account, e.g.
[0, -1, 3.14, 0/0, -100, 10, 0.2]I've tried different numbers, and it always acts as if the 0s aren't there and sorts the numbers correctly otherwise. Anyone know why?
You're getting a lexicographical sort (e.g. convert objects to strings, and sort them in dictionary order), which is the default sort behavior in Javascript:
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/sort
array.sort([compareFunction])Parameters
compareFunction
Specifies a function that defines the sort order. If omitted, the array is sorted lexicographically (in dictionary order) according to the string conversion of each element.
In the ECMAscript specification (the normative reference for the generic Javascript), ECMA-262, 3rd ed., section 15.4.4.11, the default sort order is lexicographical, although they don't come out and say it, instead giving the steps for a conceptual sort function that calls the given compare function if necessary, otherwise comparing the arguments when converted to strings:
13. If the argument comparefn is undefined, go to step 16.
14. Call comparefn with arguments x and y.
15. Return Result(14).
16. Call ToString(x).
17. Call ToString(y).
18. If Result(16) < Result(17), return −1.
19. If Result(16) > Result(17), return 1.
20. Return +0.
The default sort for arrays in Javascript is an alphabetical search. If you want a numerical sort, try something like this:
var a = [ 1, 100, 50, 2, 5];
a.sort(function(a,b) { return a - b; });
Comments
You can use a sort function :
var myarray=[25, 8, 7, 41]
myarray.sort( function(a,b) { return a - b; } );
// 7 8 25 41
Look at http://www.javascriptkit.com/javatutors/arraysort.shtml
try this:
a = new Array();
a.push(10);
a.push(60);
a.push(20);
a.push(30);
a.push(100);
a.sort(Test)
document.write(a);
function Test(a,b)
{
return a > b ? true : false;
}
6 Comments
Samir Adel
check code here: jsfiddle.net/8yxtg/1
pimvdb
First,
a > b ? false : true can be simplified to a < b. Second, you actually need to return -1, 0 or 1 so this is not completely correct (although it might work fine).
sstur
The sort function should return -1, 0 or 1 (not true/false). Most implementations will actually accept <any-negative-number>, 0 or <any-positive-number> which is why
return a-b usually works for numbers.
Max
codereturn a - bcode does not manage correctly negative numbers... a < b does.
semicolon
@Max uhh... it manages negative numbers just fine, try it.
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Array.sortsorts alphabetically, not numerically. For numeric sort:a.sort(function(a,b){return a-b}).