Ruby: counting unique elements and their occurrence in an array

Question

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

for instance

['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 reading 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 another solution with a reduction 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

The following should be done:

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

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

From the comments, the following one liner also does the same:

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

Answer 4

Not really. If you need a one-line solution, perhaps this will be the shortest (though not the most efficient):

 src = ['A','A','A','A','B','B','C'] Hash[src.group_by { |x| x }.map { |k, v| [k, v.length] }]