From: Carl Porth <badcarl@...>
Date: 2007-10-10T06:56:22+09:00
Subject: Re: Finding shared elements between to arrays.

I think the operation you are looking for is a set intersection.  In
Ruby, it is the & method.

>> ['a', 'b', 'c', 'd'] & ['c', 'd', 'e', 'f']
=> ["c", "d"]

Carl

On Oct 9, 2:46 pm, Sebastian probst Eide
<sebastian.probst.e...@gmail.com> wrote:
> Hi
> I am wondering if there is a really smart built in way to get an array
> which has the elements shared by two other arrays? I made two
> "solutions" myself, but I am wondering what other people are using, and
> if there is a preferred solution to the task? array.union(other_array)
> or something like that?
>
> Well... here are the two solutions that seemed the most obvious to me. I
> profiled them and the second one performed a little better:
>
> a1 = ['a', 'b', 'c', 'd']
> a2 = ['c', 'd', 'e', 'f']
> a3 = []
>
> #Solution 1
> a1.each { |e| a3 << e if a2.include?(e) }
>
> #Solution 2
> a3 = a1.map { |e| e if a2.include?(e) }
> a3.compact!
>
> Info from the profiler:
>   %   cumulative   self              self     total
>  time   seconds   seconds    calls  ms/call  ms/call  name
>  41.56    29.29     29.29   400000     0.07     0.11  Array#include?
>  28.31    49.24     19.95   100000     0.20     0.68  Array#each
>  22.06    64.79     15.55  1100000     0.01     0.01  String#==
>   4.19    67.74      2.95   200000     0.01     0.01  Array#<<
>   3.89    70.48      2.74        1  2740.00 70480.00  Integer#upto
>   0.00    70.48      0.00        1     0.00 70480.00  #toplevel
>
>  %   cumulative   self              self     total
>  time   seconds   seconds    calls  ms/call  ms/call  name
>  43.82    28.24     28.24   400000     0.07     0.11  Array#include?
>  23.32    43.27     15.03  1100000     0.01     0.01  String#==
>  22.25    57.61     14.34   100000     0.14     0.58  Array#map
>   8.50    63.09      5.48        1  5480.00 64450.00  Integer#upto
>   2.11    64.45      1.36   100000     0.01     0.01  Array#compact!
>   0.00    64.45      0.00        1     0.00 64450.00  #toplevel
>
> Thanks in advance!
>
> Best regards
> Sebastian
> --
> Posted viahttp://www.ruby-forum.com/.