Sorting an array of strings in Ruby

Question

I have learned two array sorting methods in Ruby:

array = ["one", "two", "three"] array.sort.reverse! 

or:

array = ["one", "two", "three"] array.sort { |x,y| y<=>x } 

And I am not able to differentiate between the two. Which method is better and how exactly are they different in execution?

Answer 1

Both lines do the same (create a new array, which is reverse sorted). The main argument is about readability and performance. array.sort.reverse! is more readable than array.sort{|x,y| y<=>x} - I think we can agree here.

For the performance part, I created a quick benchmark script, which gives the following on my system (ruby 1.9.3p392 [x86_64-linux]):

                              user     system      total        real array.sort.reverse        1.330000   0.000000   1.330000 (  1.334667) array.sort.reverse!       1.200000   0.000000   1.200000 (  1.198232) array.sort!.reverse!      1.200000   0.000000   1.200000 (  1.199296) array.sort{|x,y| y<=>x}   5.220000   0.000000   5.220000 (  5.239487) 

Run times are pretty constant for multiple executions of the benchmark script.

array.sort.reverse (with or without !) is way faster than array.sort{|x,y| y<=>x}. Thus, I recommend that.

---

Here is the script as a Reference:

#!/usr/bin/env ruby require 'benchmark'  Benchmark.bm do|b|   master = (1..1_000_000).map(&:to_s).shuffle   a = master.dup   b.report("array.sort.reverse      ") do     a.sort.reverse   end    a = master.dup   b.report("array.sort.reverse!     ") do     a.sort.reverse!   end    a = master.dup   b.report("array.sort!.reverse!    ") do     a.sort!.reverse!   end    a = master.dup   b.report("array.sort{|x,y| y<=>x} ") do     a.sort{|x,y| y<=>x}   end end 

Answer 2

There really is no difference here. Both methods return a new array.

For the purposes of this example, simpler is better. I would recommend array.sort.reverse because it is much more readable than the alternative. Passing blocks to methods like sort should be saved for arrays of more complex data structures and user-defined classes.

Edit: While destructive methods (anything ending in a !) are good for performance games, it was pointed out that they aren't required to return an updated array, or anything at all for that matter. It is important to keep this in mind because array.sort.reverse! could very likely return nil. If you wish to use a destructive method on a newly generated array, you should prefer calling .reverse! on a separate line instead of having a one-liner.

Example:

array = array.sort array.reverse! 

should be preferred to

array = array.sort.reverse!