Descending sort by value of a Hash in Ruby

Question

My input hash: h = { "a" => 20, "b" => 30, "c" => 10 }

Ascending sort: h.sort {|a,b| a[1]<=>b[1]} #=> [["c", 10], ["a", 20], ["b", 30]]

But, I need [["b", 30], ["a", 20], ["c", 10]]

How is can we make it work the other way around, what does <=> mean?

Answer 1

You can have it cleaner, clearer and faster, all at once! Like this:

h.sort_by {|k,v| v}.reverse 

I benchmarked timings on 3000 iterations of sorting a 1000-element hash with random values, and got these times:

h.sort {|x,y| -(x[1]<=>y[1])} -- 16.7s h.sort {|x,y| y[1] <=> x[1]} -- 12.3s h.sort_by {|k,v| -v} -- 5.9s h.sort_by {|k,v| v}.reverse -- 3.7 

Answer 2

h.sort {|a,b| b[1]<=>a[1]}