Sorting a hash by value then by key (but the key is reversed)

Question

The title says it all.

total = {"Bob"=>37, "Alice"=>42, "Carl"=>42}

I want to sort it by value, and then by key, but with the key in descending order.

Like this:

{"Bob"=>37, "Carl"=>42, "Alice"=>42}

I tried:

return total.sort_by { |k, v| [v, k] }

But from here I don't know how to reverse k...

score 5 · Accepted Answer · edited Jun 20 '20 at 09:12

5

Use sort:

total = {"Bob"=>37, "Alice"=>42, "Carl"=>42}
total.sort { |(k1, v1), (k2, v2)| [v1, k2] <=> [v2, k1] }.to_h
# => {"Bob"=>37, "Carl"=>42, "Alice"=>42}

First, sort by values (v1 <=> v2) and then reverse sort by keys (k2 <=> k1), and since we need it simultaneously, put it into array.

EDIT: @Mirror318, it just looks scary, take a look at the excellent explanation here: What is the Ruby <=> (spaceship) operator?

edited Jun 20 '20 at 09:12

Community

answered Sep 16 '15 at 08:47

Alexey Shein

This makes me want to crawl into a corner >< how do you wrap your head around all this? – Mirror318 Sep 16 '15 at 09:13
@Mirror318 `sort_by { |x| x }` is roughly equivalent to `sort { |a, b| a <=> b }`. Expand your code accordingly, and you almost have the answer. – Stefan Sep 16 '15 at 09:29
Mirror, it won't be long before you will see this as routine. – Cary Swoveland Oct 04 '15 at 20:43

Cary Swoveland · Answer 2 · 2020-11-03T23:46:03.187

3

Another way:

total.sort_by { |k,v| [-v,k] }.reverse.to_h
  #=> {"Bob"=>37, "Carl"=>42, "Alice"=>42}

edited Nov 03 '20 at 23:46

answered Oct 04 '15 at 20:53

Cary Swoveland

score -1 · Answer 3 · answered Sep 16 '15 at 09:14

-1

If you're using ruby >= 2.1, then just call to_h on sorted array of tuples:

total = {"Bob"=>37, "Alice"=>42, "Carl"=>42}
total.sort_by{|k, v| [v, k]}.to_h

Else call Hash.new:

total = {"Bob"=>37, "Alice"=>42, "Carl"=>42}
Hash.new total.sort_by{|k, v| [v, k]}.to_h

answered Sep 16 '15 at 09:14

Aetherus

3 Answers3