I'm going ga-ga here, trying to get these suggestions to work with Active Perl (Build 813) under WinXP...

Example 1: 

my @arr = qw( and you will be pleased with the results );
#             0   0   1    0  1       0    1   1
my $mask = 0x2b;

sub mask_array (\@$) {
  my( $arr, $mask ) = @_;
  my @want = split '', unpack( "b*", $mask );
  return @{ $arr }[ grep { $want[ $_ ] } 0..$#{ $arr } ];
}

my @result = mask_array @arr => $mask;

foreach (@result) {
   printf("%s\n", $_);
}

[download]
This is the same as is posted earlier in the discussion. This version is broken as the output is:
will
pleased
with

Example 2: 

my @arr = qw( and you will be pleased with the results );
#             0   0   1    0  1       0    1   1
my $mask = "\x2b";

my @new = do { my $i = 0; map { vec($mask, $#arr - $i++, 1) ? $_ : () 
+} @arr };

foreach (@new) {
   printf("%s\n", $_);
}

[download]
This code is the same as entered above in the discussion; its output is correct:
will
pleased
the
results

Example 3: 

@arr = qw( and you will be pleased with the results XX YY AA BB );
# \x2b     0   0   1    0  1       0    1   1       0  0  1  0 
# \x2b20   0   0   1    0  0       0    1   0       1  0  1  1
$mask = "\x2b20";

@new = do { my $i = 0; map { vec($mask, $#arr - $i++, 1) ? $_ : () } @
+arr };

foreach (@new) {
   printf("%s\n", $_);
}

[download]
The main code of this version is the same as Example 2 but I'm trying to work out how the bit map is supposed to work. This version breaks when there is more than 8 elements from which to select; its output is:
will
the
XX
AA
BB

I'm not flash on this bit manipulation and working with byte boundaries, etc... but these approaches look like they'd be useful with my current job: to be able to specify an arbitrary list of items to select from an arbitrarily long array.

Any further suggestions/explanations?

Thanks.

In reply to Re: Taking arbitrary elements from an array by ozboomer
in thread Taking arbitrary elements from an array by grinder

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