Ruby - find the key(s) of the largest value(s) of a hash

Question

I have a hash and I want to return the key(s) (or key/value pair(s)) of the max value(s) of the hash. So, if there is only one true max, it will return that one key; however, if there are multiple key/value pairs with the same value, it will return all of these keys. How can I accomplish this in Ruby?

my_hash.max_by {|k,v| v} #only returns one key/value pair

i guess its the same question answered here http://stackoverflow.com/questions/6040494/how-to-find-the-key-of-the-largest-value-hash — yasir hashmi, Oct 22 '12 at 05:29
What kind of values are you storing in your hash? Are you only dealing with integers? — Amir Rubin, Oct 22 '12 at 05:30
@yasirhashmi yes, same except I don't want to return only one, I want to return multiple k/v pairs if they have the same value. — diasks2, Oct 22 '12 at 05:32
@AmirRubin the key is a string, value is a floating decimal. — diasks2, Oct 22 '12 at 05:33

oldergod · Accepted Answer · 2012-10-22T07:59:23.663

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If you want all pairs, I would do something like

max = my_hash.values.max
Hash[my_hash.select { |k, v| v == max}]

edited Oct 22 '12 at 07:59

answered Oct 22 '12 at 05:36

oldergod

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Why === ? I think that might not do what you think it does. – pguardiario Oct 22 '12 at 07:39

score 2 · Answer 2 · answered Oct 22 '12 at 20:48

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A single liner:

my_hash.reduce({}){|h,(k,v)| (h[v] ||= []) << k;h}.max

irb
> z = {:tree => 3, :two => 2, 'three' => 3}

>  z.reduce({}){|h,(k,v)| (h[v] ||= []) << k;h}.max
[3, [:tree, "three"]]

answered Oct 22 '12 at 20:48

ShadyKiller

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Ruby - find the key(s) of the largest value(s) of a hash

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