How to sort a Ruby Hash by number value?

Since value is the last entry, you can do:

metrics.sort_by(&:last)

Already answered but still. Change your code to:

metrics.sort {|a1,a2| a2[1].to_i <=> a1[1].to_i }

Converted to strings along the way or not, this will do the job.

No idea how you got your results, since it would not sort by string value... You should reverse a1 and a2 in your example

Best way in any case (as per Mladen) is:

metrics = {"sitea.com" => 745, "siteb.com" => 9, "sitec.com" => 10 }
metrics.sort_by {|_key, value| value}
  # ==> [["siteb.com", 9], ["sitec.com", 10], ["sitea.com", 745]]

If you need a hash as a result, you can use to_h (in Ruby 2.0+)

metrics.sort_by {|_key, value| value}.to_h
  # ==> {"siteb.com" => 9, "sitec.com" => 10, "sitea.com", 745}