Ruby: Count unique elements and their occurences in an array [duplicate]

Question

Is there a method in Ruby that takes an array, and counts all unique elements and their occurrences and passes them back as a hash?

For example

  ['A','A','A','A','B','B','C'].method
> {'A' => 4, 'B' => 2, 'C' => 1}

Something like that.

Answer 1

['A','A','A','A','B','B','C'].group_by{|e| e}.map{|k, v| [k, v.length]}.to_h

Answer 2

This is the easiest readable for me:

src = ['A','A','A','A','B','B','C']
src.group_by(&:to_s).map { |a| [a[0], a[1].count] }.to_h

Or here is another solution with reduce method:

src.reduce({}) { |b, a| b.merge({a => (b[a] || 0) + 1}) }

Or:

src.reduce(Hash.new(0)) { |b, a| b.merge({a => b[a] + 1}) }

Answer 3

Following should do:

counts = Hash.new(0)
['A','A','A','A','B','B','C'].each { |name| counts[name] += 1 }

counts => {"A"=>4, "B"=>2, "C"=>1}

From comments, following one liner also do the same:

['A','A','A','A','B','B','C'].each_with_object(Hash.new(0)) { |l, o| o[l] += 1 }