Sorting array of float point numbers

Question

I have an array of float point numbers:

[ 82.11742562118049, 28.86823689842918, 49.61295450928224, 5.861613903793295 ]

After running sort() on the array I get this:

[ 28.86823689842918, 49.61295450928224, 5.861613903793295, 82.11742562118049 ]

Notice how 5.8... is bigger than 49.6... for JavaScript (Node). Why is that?

How can I correctly sort this numbers?

Use `arr.sort(function (a, b) { return a-b; });`. As it stands, the values are being sorted alphabetically. "2" comes before "4", which comes before "5", which comes before "8" (the comparison is the first "letter" of each number...until they match, then it compares the next letter, and so on) — Ian, Aug 28 '13 at 19:45
For reference: http://www.w3schools.com/jsref/jsref_sort.asp. By default javascript's array sort method sorts alphabetically and ascending. Hence, why you pass in the sort method provided by @Ian — Suvi Vignarajah, Aug 28 '13 at 19:51
Generally, don't reference w3 schools as they can be incorrect for a wide range of things. — jtromans, Oct 10 '13 at 13:12

score 56 · Accepted Answer · edited Aug 28 '13 at 19:57

56

Pass in a sort function:

[….].sort(function(a,b) { return a - b;});

results:

[5.861613903793295, 28.86823689842918, 49.61295450928224, 82.11742562118049]

From MDN:

If compareFunction is not supplied, elements are sorted by converting them to strings and comparing strings in lexicographic ("dictionary" or "telephone book," not numerical) order.

edited Aug 28 '13 at 19:57

answered Aug 28 '13 at 19:49

dc5

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parenthesizes don't match. – zs2020 Aug 28 '13 at 19:54
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@CrazyTrain - thanks for the edit. thought I was going blind there :) – dc5 Aug 28 '13 at 20:00
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Here's a shorter version if you're into that sort of thing: `yourArray.sort( (a,b) => a-b )` – Travis Heeter Jun 26 '21 at 10:29

score 5 · Answer 2 · answered Aug 28 '13 at 19:52

5

The built in JS sort function treats everything as strings. Try making your own:

var numbers = new Array ( 82.11742562118049, 28.86823689842918, 49.61295450928224, 5.861613903793295 );

function sortFloat(a,b) { return a - b; }

numbers.sort(sortFloat);

answered Aug 28 '13 at 19:52

Matt Pavelle

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you should use array literal instead. `[...]`, not `new Array(...)` – Björn Roberg Aug 28 '13 at 19:58

Sorting array of float point numbers

2 Answers2

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