This blog is part of our Ruby 2.7 series. Ruby 2.7.0 was released on Dec 25, 2019.

Let’s say that we have to find the frequency of each element of an array.

Before Ruby 2.7, we could have achived it using group_by or inject.

irb> scores = [100, 35, 70, 100, 70, 30, 35, 100, 45, 30]

# we can use group_by to group the scores

irb> scores.group_by { |v| v }.map { |k, v| [k, v.size] }.to_h
=> {100=>3, 35=>2, 70=>2, 30=>2, 45=>1}

# or we can use inject to group the scores

irb> scores.inject(Hash.new(0)) {|hash, score| hash[score] += 1; hash }
=> {100=>3, 35=>2, 70=>2, 30=>2, 45=>1}

Ruby 2.7

Ruby 2.7 adds Enumerable#tally which can be used to find the frequency. Tally makes the code more readable and intutive. It returns a hash where keys are the unique elements and values are its corresponding frequency.

irb> scores = [100, 35, 70, 100, 70, 30, 35, 100, 45, 30]
irb> scores.tally
=> {100=>3, 35=>2, 70=>2, 30=>2, 45=>1}

Check out the github commit for more details on this.