Ruby hash: return keys with highest value

Question

I want to return a hash key/value pair based on max key value. I know max_by works, but it stops at the first result. How can I return all results in the event of a tie?

{
  foo: 1,
  bar: 3,
  baz: 3
}.max_by { |key, value| value }

#=> [:bar 3] # Only bar comes back, but baz also has a value of 3.

Arup Rakshit · Accepted Answer · 2014-04-02 17:46:20Z

1

I'd do :

hash = {
         foo: 1,
         bar: 3,
         baz: 3
       }

hash.group_by { |_,value| value }.max_by { |key,_| key }.last
# => [[:bar, 3], [:baz, 3]]

Breaking of the above code :

hash.group_by { |_,v| v } 
# => {1=>[[:foo, 1]], 3=>[[:bar, 3], [:baz, 3]]}
hash.group_by { |_,v| v }.max_by { |k,_| k }
# => [3, [[:bar, 3], [:baz, 3]]]

edited Apr 2, 2014 at 17:46

answered Apr 2, 2014 at 17:27

Arup Rakshit

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3 Comments

Jumbalaya Wanton Over a year ago

Thanks. What's the _ meant to be? Is it the key? Why not use key?

Jumbalaya Wanton Over a year ago

+1! Thank you. I was not aware of the _. Is it documented any where?

Arup Rakshit Over a year ago

@JumbalayaWanton Yes it is.. But I need to search.. :)

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