# Making a count of unique elements in an array

Given an array, I need to produce a two-dimensional resulting array
where each pair consists of a unique element from the original array
and the number of times that element appears.

I found two ways to do this. Is one of them better? Is there a better
way?

arr = %w{a b b c c d e e e}
p arr
p arr.uniq.map {|e| [e, (arr.select {|ee| ee == e}).size ]}
counter = {}
arr.each {|e| counter[e] += 1 rescue counter[e] = 1 }
p counter.to_a

outputs:

[“a”, “b”, “b”, “c”, “c”, “d”, “e”, “e”, “e”]
[[“a”, 1], [“b”, 2], [“c”, 2], [“d”, 1], [“e”, 3]]
[[“a”, 1], [“b”, 2], [“c”, 2], [“d”, 1], [“e”, 3]]

Dan K. wrote:

counter = {}
arr.each {|e| counter[e] += 1 rescue counter[e] = 1 }
p counter.to_a

outputs:

[“a”, “b”, “b”, “c”, “c”, “d”, “e”, “e”, “e”]
[[“a”, 1], [“b”, 2], [“c”, 2], [“d”, 1], [“e”, 3]]
[[“a”, 1], [“b”, 2], [“c”, 2], [“d”, 1], [“e”, 3]]

I like #inject 1-liners:

arr = %w{a b b c c d e e e}
=> [“a”, “b”, “b”, “c”, “c”, “d”, “e”, “e”, “e”]

arr.inject(Hash.new(0)) {|h,x| h[x]+=1;h}
=> {“a”=>1, “b”=>2, “c”=>2, “d”=>1, “e”=>3}

arr.inject(Hash.new(0)) {|h,x| h[x]+=1;h}.to_a
=> [[“a”, 1], [“b”, 2], [“c”, 2], [“d”, 1], [“e”, 3]]

arr.inject(Hash.new(0)) {|h,x| h[x]+=1;h}.sort
=> [[“a”, 1], [“b”, 2], [“c”, 2], [“d”, 1], [“e”, 3]]

Kind regards

``robert``

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