Ruby on Rails sort_by vs sort

Posted on 05 February 2010

Given the choice when sorting arrays in Ruby it's typically better to use sort_by rather than sort.

sort_by uses the Schwartzian transform technique that is a Perl programming idiom used to improve the efficiency of sorting a list of items.

You can use sort_by like so...

foo.sort_by(&:bar)

The equivalent using sort would look like...

foo.sort{|a,b| b.bar <=> a.bar}

However, using sort will mean that the method bar is called twice for each comparison and therein lies the inefficiency.

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Comments...

• Thanks for the straightforward explanation! It was useful to me.

  Evan at 18 Feb 11 at 15:20

• When I try to use sort_by:

  "NoMethodError: You have a nil object when you didn't expect it!
  You might have expected an instance of Array.
  The error occurred while evaluating nil.<=>
  from (irb):42:in `sort_by'
  from (irb):42"

  What I doing wrong?

  Sergey at 18 Aug 11 at 11:21

• Thanks Paul! I just used this and it was great! I've always hated all the lengthy syntax required for the normal sort method.

  Ammar Yousuf at 02 Nov 11 at 18:24

• Thanks. Was helpful.

  A Person at 06 Dec 11 at 10:52