CODEWITHSUNDEEP
rubyhash
JZ.
JZ.

Reputation: 21877

How to find the key of the largest value hash?

I have the following hash {"CA"=>2, "MI"=>1, "NY"=>1}

How can I return the maximum key value pair using ruby? I would like it to return "CA"

Upvotes: 128

Views: 95628

Answers (6)

Tiberiu Macelaru
Tiberiu Macelaru

Reputation: 511

I found this way , return the key of the first max value 

hash.key(hash.values.max)

Upvotes: 49

JP Duffy
JP Duffy

Reputation: 1368

I did this today on a similar problem and ended up with this:

hash = { "CA"=>2, "MI"=>1, "NY"=>1 }

hash.invert.max&.last
=> "CA"

For Ruby less than 2.3 you can replace &.last with .try(:last) Either one is just a safeguard for if your source hash is empty: {}

Upvotes: 4

Linju
Linju

Reputation: 335

If you want to retrieve more than one key value pair based on order(second largest, smallest etc.), a more efficient way will be to sort the hash once and then get the desired results.

def descend_sort(hash)
   hash = hash.sort_by {|k,v| v}.reverse
end

Key of largest value

puts *hash[0][0]

Get max and min

puts *hash[0], *hash[hash.length-1]

2nd largest key value pair

Hash[*hash[1]]

To convert the hash array back into a hash

hash.to_h

Upvotes: 5

K. George Pradhan
K. George Pradhan

Reputation: 173

Another way could be as follows: 

hash.each { |k, v| puts k if v == hash.values.max }

This runs through each key-value pair and returns (or in this case puts's) the key(s) where the value is equal to the max of all values. This should return more than one key if there's a tie.

Upvotes: 14

Hck
Hck

Reputation: 9167

This will return max hash key-value pair depending on the value of hash elements:

def largest_hash_key(hash)
  hash.max_by{|k,v| v}
end

Upvotes: 263

Sam 山
Sam 山

Reputation: 42865

This will return the last key of the hash sorted by size; however, there might be two keys with the same value.

def largest_hash_key(hash)
  key = hash.sort{|a,b| a[1] <=> b[1]}.last
  puts key
end

hash = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
largest_hash_key(hash)

Upvotes: -3

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