From: Sebastian probst Eide <sebastian.probst.eide@...>
Date: 2007-10-10T06:46:59+09:00
Subject: Finding shared elements between to arrays.

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
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