If you construct the hash before testing the results are somewhat different

I used the following, a slight change from your program

Assuming that you can use a hash table elsewhere in the program (and why not?) hash tables appear to make more sense when looked at this way. I cannot see any use for dynamically creating a hash table just for one search and, if you are going to search a hash you may as well structure your data into a hash.

Of course there are exceptions to this, there are exceptions to everything in the perl world (TIMTOWTDI)

anyway, the data:

  use Benchmark;
  use strict;

  # Times array searches.  Assumes search element is in the
  # dead center of the array

  my $x;
  my @array;
  my %hash;

  for (10, 50, 100, 500, 1000, 5000)
  {
      @array = 1 .. $_;
      $x = $_ / 2;
      $hash{$_}++ for @array;

      print "Array size is $_\n";

      timethese(5000, {
          'grep' => \&grep_test,
          hash => \&hash_test,
          manual => \&manual_test
      });
  }

  sub grep_test
  {
      return 1 if grep { $x == $_ } @array;
  }

  sub hash_test
  {
      return 1 if $hash{$x};
  }

  sub manual_test
  {
      for (@array) { return 1 if $x == $_ }
  } 


Array size is 10
Benchmark: timing 5000 iterations of grep, hash, manual...
      grep:  0 wallclock secs ( 0.03 usr +  0.00 sys =  0.03 CPU)
            (warning: too few iterations for a reliable count)
      hash:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
            (warning: too few iterations for a reliable count)
    manual:  0 wallclock secs ( 0.04 usr +  0.00 sys =  0.04 CPU)
            (warning: too few iterations for a reliable count)
Array size is 50
Benchmark: timing 5000 iterations of grep, hash, manual...
      grep:  0 wallclock secs ( 0.15 usr +  0.00 sys =  0.15 CPU)
            (warning: too few iterations for a reliable count)
      hash:  0 wallclock secs ( 0.01 usr +  0.00 sys =  0.01 CPU)
            (warning: too few iterations for a reliable count)
    manual:  0 wallclock secs ( 0.11 usr +  0.00 sys =  0.11 CPU)
            (warning: too few iterations for a reliable count)
Array size is 100
Benchmark: timing 5000 iterations of grep, hash, manual...
      grep:  0 wallclock secs ( 0.27 usr +  0.00 sys =  0.27 CPU)
            (warning: too few iterations for a reliable count)
      hash:  0 wallclock secs ( 0.02 usr +  0.00 sys =  0.02 CPU)
            (warning: too few iterations for a reliable count)
    manual:  1 wallclock secs ( 0.20 usr +  0.00 sys =  0.20 CPU)
            (warning: too few iterations for a reliable count)
Array size is 500
Benchmark: timing 5000 iterations of grep, hash, manual...
      grep:  1 wallclock secs ( 1.39 usr +  0.00 sys =  1.39 CPU)
      hash:  0 wallclock secs (-0.00 usr +  0.00 sys = -0.00 CPU)
            (warning: too few iterations for a reliable count)
    manual:  1 wallclock secs ( 0.90 usr +  0.00 sys =  0.90 CPU)
Array size is 1000
Benchmark: timing 5000 iterations of grep, hash, manual...
      grep:  3 wallclock secs ( 2.79 usr +  0.00 sys =  2.79 CPU)
      hash:  0 wallclock secs ( 0.02 usr +  0.00 sys =  0.02 CPU)
            (warning: too few iterations for a reliable count)
    manual:  2 wallclock secs ( 1.77 usr +  0.00 sys =  1.77 CPU)
Array size is 5000
Benchmark: timing 5000 iterations of grep, hash, manual...
      grep: 15 wallclock secs (15.39 usr +  0.00 sys = 15.39 CPU)
      hash:  0 wallclock secs ( 0.01 usr +  0.00 sys =  0.01 CPU)
            (warning: too few iterations for a reliable count)
    manual: 10 wallclock secs ( 9.03 usr +  0.05 sys =  9.08 CPU)
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