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.
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3Note that since Ruby 2.7 the tally method does exactly this. docs.ruby-lang.org/en/3.0.0/Enumerable.html#method-i-tallyAndrew– Andrew2021-10-19 04:15:10 +00:00Commented Oct 19, 2021 at 4:15
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4 Answers
['A','A','A','A','B','B','C'].group_by{|e| e}.map{|k, v| [k, v.length]}.to_h
1 Comment
sawa
@GreyCat A simple ruby question should by default be assuming the latest version. When older versions are used, special mentioning should be done. To you, does a TV mean a black and white, vacuum-tube operated one? Do I need to particularly say "color TV" to distinguish one from a black and white TV?
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}) }
Comments
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 }
1 Comment
Alexander Kireyev
Or in one line
['A','A','A','A','B','B','C'].each_with_object(Hash.new(0)) { |l, o| o[l] += 1 }Not really. If you want one-liner solution, probably this one would be the shortest (albeit not most efficient):
src = ['A','A','A','A','B','B','C']
Hash[src.group_by { |x| x }.map { |k, v| [k, v.length] }]
