suppose I have an array [1,2,3,1,5,2]. Here 1 and 2 are the repeated elements. I want to get a new array [1,2].
How do I do that in ruby ??
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@mihai, thanks, voted to close, now you can safely remove your answer.tokland– tokland2011-12-10 19:06:58 +00:00Commented Dec 10, 2011 at 19:06
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2 Answers
arr = [1,2,3,1,5,2]
arr.group_by {|e| e}.map { |e| e[0] if e[1][1]}.compact
Pretty ugly... but does the job without an n+1 problem.
arr = [1,2,3,1,5,2]
arr.select { |x| arr.count(x) > 1 } .uniq
A longer solution using reduce should be quicker.
arr.reduce [{}, []] do |(seen, out), cur|
case seen[cur]
when :seen then
[seen.merge({cur => :added}), out << cur]
when :added then
[seen, out]
else
[seen.merge({cur => :seen}), out]
end
end.last
4 Comments
tokland
I wrote something similar in the duplicated question: stackoverflow.com/a/8459032/188031. But I see some problems here: 1) you are using an array object to test inclussion, which is O(n), a hash or set would be more suitable. 2) you can safely remove the
uniq. 3) Use arguments expansion instead of acc[0]/acc[1].
Jan
@tokland, thanks for the comment. 1) I've switched to
Hash. 2) No, unfortunately not. See [1,1,1]. 3) Good point!Jan
After the last change
uniq isn't necessary any longer.tokland
you are right! now I have to check my solution.