What is the key() method of a hash value in Ruby?

Overview

In Ruby, the key() method of a hash returns the key for the first-found entry with the given value. The given value is passed as an argument to this method.

Syntax

hash.key(value)

Parameters

value: This is the value whose key we want to find.

Return value

This method returns the key for the first-found entry with the value value. Nil is returned if no such value exists.

Code example

# create hashes
h1 = {one: 1, two: 2, three: 3}
h2 = {name: "Okwudili", stack: "ruby"}
h3 = {"foo": 0, "bar": 1}
h4 = {M:"Mango", A: "Apple", B: "Banana"}
# find key entries 
# and print results
puts "#{h1.key(2)}\n"          # two
puts "#{h2.key('Okwudili')}\n" # name
puts "#{h3.key(5)}"            # nil
puts "#{h4.key("Apple")}"      # A

Code explanation

  • Lines 2–5: We create several hashes.
  • Lines 9–12: We invoke the key() method, along with some arguments, on the hashes to get some keys. Then, we print the results to the console.

Note: Line 11 printed nil because no key had a value of 5.

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