Sort an Array of Strings by their Integer Values

Question

Let's say I have an unsorted array from 1 to 10, as shown below...

a = ["3", "5", "8", "4", "1", "2", "9", "10", "7", "6"]

If I use the sort method on this array, it returns this...

a.sort = ["1", "10", "2", "3", "4", "5", "6", "7", "8", "9"]

As you can see, the 10, appears before the 2, which is incorrect. How can I sort these numbers so that 10 appears correctly?

EDIT: Thank you all for your responses. I should explain my problem a little better. The array I need sorted is for an e-commerce price list. So the array appears as follows...

a = ["0-10", "11-20", "21-30", "31-40" etc.]

So the strings cannot be converted to integers. I should have put this when I wrote the question. I did not think that there would be much difference in the fix. My mistake, I apologise for making this assumption! How though can I sort this array? Thanks!

I think this question has already been answered: http://stackoverflow.com/questions/1955646/sort-strings-and-numbers-in-ruby/1964686#1964686 — Klas Lindbäck, Oct 11 '11 at 13:42
I suggest you post a new question with updated description, since all the answers are base on the wrong description. — Jakub Arnold, Oct 11 '11 at 15:34
Since `#to_i` will interpret leading numeric characters in a string, the methods using `#to_i` will work for your example above. — Wizard of Ogz, Oct 11 '11 at 17:02

score 55 · Accepted Answer · answered Oct 11 '11 at 14:10

55

I'll throw another method out there since it's the shortest way I can think of

a.sort_by(&:to_i)

answered Oct 11 '11 at 14:10

Wizard of Ogz

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This is equivalent to bricker's answer, so his comment about the number of times `to_i` is called compared to Matt's solution applies here as well. – Wizard of Ogz Oct 11 '11 at 14:24
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What is `&:`? That's a new syntax to me. – nipponese Jul 18 '17 at 20:22
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@nipponese That is a good question. Here is a good thread which explains it in detail https://stackoverflow.com/questions/1961030/ruby-ampersand-colon-shortcut. – Wizard of Ogz Jul 18 '17 at 21:06

score 10 · Answer 2 · edited Oct 12 '11 at 00:24

10

As your updated question states:

array.sort_by {|elt| ary = elt.split("-").map(&:to_i); ary[0] + ary[1]}

even geekier:

array.sort_by {|elt| ary = elt.split("-").map(&:to_i).inject(&:+)}

edited Oct 12 '11 at 00:24

Harish Shetty

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answered Oct 11 '11 at 15:16

apneadiving

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score 7 · Answer 3 · answered Oct 11 '11 at 13:43

7

If you convert all strings to integers beforehand, it should work as expected:

a.map(&:to_i).sort
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

answered Oct 11 '11 at 13:43

Matt

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Doesn't really matter for such a small array, but your method would be faster than mine for large arrays, calling to_i only half as many times. +1 – bricker Oct 11 '11 at 13:56
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@bricker Matt's method also uses more memory as it creates a new array with `map` that your method doesn't. (You could use the in-place map `map!`, but that might not always be a viable option in your code) – Wizard of Ogz Oct 11 '11 at 14:13

score 6 · Answer 4 · answered Oct 11 '11 at 13:40

6

a.sort { |a,b| a.to_i <=> b.to_i }

answered Oct 11 '11 at 13:40

bricker

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use Enumerable#sort_by instead – tokland Oct 11 '11 at 14:23
Why? The sort method works perfectly, I'd like to know why you recommend sort_by. – bricker Oct 11 '11 at 15:08
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By definition xs.sort { |a, b| a.method <=> b.method } is totally equivalent to xs.sort_by(&:method). Why use sort when you have a shorter built-in exactly designed for this task? If that's not enough, there are also performance reasons, c&p from the docs: "As of Ruby 1.8, the method Enumerable#sort_by implements a built-in Schwartzian Transform, useful when key computation or comparison is expensive." – tokland Oct 11 '11 at 15:11
@tokland Thanks for the point about Schwartzian transforms occurring behind the scenes. – Wizard of Ogz May 01 '12 at 14:31

score 2 · Answer 5 · answered Sep 23 '19 at 13:34

2

Another option, that can be used in your example or others arrays like

a = ["teste", "test", "teste2", "tes3te", "10teste"]

is:

a.sort_by! {|s| s[/\d+/].to_i}

answered Sep 23 '19 at 13:34

Jéssica Antunes

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score 1 · Answer 6 · answered Oct 11 '11 at 13:41

The reason for this behavior is that you have an array of strings and the sort that is being applied is string-based. To get the proper, numeric, sorting you have to convert the strings to numbers or just keep them as numbers in the first place. Is there a reason that your array is being populate with strings like this:

a = ["3", "5", "8", "4", "1", "2", "9", "10", "7", "6"]

Rather than numbers like this:

a = [3, 5, 8, 4, 1, 2, 9, 1, 7, 6]

?

Sai Siva Teja · Answer 7 · 2021-01-07T18:57:00.480

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For the special case (e-commerce price list) you mentioned

a = ["0-10", "11-20", "21-30", "31-40"]

let's add a few more values to this array (as it was mentioned as price list). so

a = ["0-10", "11-20", "120-150", "110-120", "21-30", "31-40"]

we can sort such an array using the following

a.sort.sort_by(&:length)

edited Jan 07 '21 at 18:57

answered Dec 11 '20 at 08:47

Sai Siva Teja

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score 0 · Answer 8 · answered Oct 11 '11 at 13:40

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The cheap way would be to zero fill on the left and make all numbers 2 digit.

answered Oct 11 '11 at 13:40

Thom

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Cheap & best way is to sort them as integers instead of strings. – bricker Oct 11 '11 at 13:43

Sort an Array of Strings by their Integer Values

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