From: Robert Klemme <bob.news@...>
Date: 2006-01-09T19:13:02+09:00
Subject: Re: Making a count of unique elements in an array

Dan Kohn wrote:
> 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]]

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