27

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!

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5
  • I think this question has already been answered: stackoverflow.com/questions/1955646/… Commented Oct 11, 2011 at 13:42
  • Just posted an answer to your updated question Commented Oct 11, 2011 at 15:21
  • I suggest you post a new question with updated description, since all the answers are base on the wrong description. Commented Oct 11, 2011 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. Commented Oct 11, 2011 at 17:02
  • I dont think it will. '10-11'.to_i is 10. try it Commented Apr 1, 2015 at 21:02

8 Answers 8

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55

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

a.sort_by(&:to_i)
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3 Comments

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.
What is &:? That's a new syntax to me.
@nipponese That is a good question. Here is a good thread which explains it in detail stackoverflow.com/questions/1961030/….
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(&:+)}
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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]
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2 Comments

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 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)
6 
a.sort { |a,b| a.to_i <=> b.to_i }
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4 Comments

use Enumerable#sort_by instead
Why? The sort method works perfectly, I'd like to know why you recommend sort_by.
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 Thanks for the point about Schwartzian transforms occurring behind the scenes.
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}
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1

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]

?

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0

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

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1 Comment

Cheap & best way is to sort them as integers instead of strings.
0

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)
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