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"
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4What if there are multiple keys with the same largest value?Gabe– Gabe2011-05-18 06:03:06 +00:00Commented May 18, 2011 at 6:03
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6 Answers
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
5 Comments
justingordon
worth noting you get back a 2 element array with [key, value]
nfriend21
hash.max_by{ |k,v| v }[0] gives the key.
Robbie Guilfoyle
Also worth noting a tie will go to first in order of position.
mahemoff
You can also do hash.max_by(&:last) for the pair and hash.max_by(&:last).first for the key.
Scott Jodoin
Be warned that this does not work if the hash is empty.
I found this way , return the key of the first max value
hash.key(hash.values.max)
1 Comment
Schwern
While
hash[key] is very efficient, hash.key(value) has to search the whole hash. This answer searches the hash twice: first to find the maximum value, then to find the key which matches that value.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.
1 Comment
user229044
This is a really remarkably inefficient solution, and it's more typing that the other much more efficient solutions.
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
Comments
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: {}
Comments
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)
1 Comment
tokland
selected answer? may_by is much better than a low-level sort. It's more compact and uses less memory than a sort+last.