Descending sort by value of a Hash in Ruby
RubySortingHashRuby Problem Overview
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?
Ruby Solutions
Solution 1 - Ruby
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
Solution 2 - Ruby
h.sort {|a,b| b[1]<=>a[1]}
Solution 3 - Ruby
<=> compares the two operands, returning -1 if the first is lower, 0 if they're equal and 1 if the first is higher. This means that you can just do -(a[1]<=>b[1]) to reverse the order.
Solution 4 - Ruby
Super simple: h.sort_by { |k, v| -v }