What is the best way to delete a value from an array in Perl?

Question

The array has lots of data and I need to delete two elements.

Below is the code snippet I am using,

my @array = (1,2,3,4,5,5,6,5,4,9);
my $element_o         


        

Answer 1

Just to be sure I have benchmarked grep and map solutions, first searching for indexes of matched elements (those to remove) and then directly removing the elements by grep without searching for the indexes. I appears that the first solution proposed by Sam when asking his question was already the fastest.

    use Benchmark;
    my @A=qw(A B C A D E A F G H A I J K L A M N);
    my @M1; my @G; my @M2;
    my @Ashrunk;
    timethese( 1000000, {
      'map1' => sub {
          my $i=0;
          @M1 = map { $i++; $_ eq 'A' ? $i-1 : ();} @A;
      },
      'map2' => sub {
          my $i=0;
          @M2 = map { $A[$_] eq 'A' ? $_ : () ;} 0..$#A;
      },
      'grep' => sub {
          @G = grep { $A[$_] eq 'A' } 0..$#A;
      },
      'grem' => sub {
          @Ashrunk = grep { $_ ne 'A' } @A;
      },
    });

The result is:

Benchmark: timing 1000000 iterations of grem, grep, map1, map2...
  grem:  4 wallclock secs ( 3.37 usr +  0.00 sys =  3.37 CPU) @ 296823.98/s (n=1000000)
  grep:  3 wallclock secs ( 2.95 usr +  0.00 sys =  2.95 CPU) @ 339213.03/s (n=1000000)
  map1:  4 wallclock secs ( 4.01 usr +  0.00 sys =  4.01 CPU) @ 249438.76/s (n=1000000)
  map2:  2 wallclock secs ( 3.67 usr +  0.00 sys =  3.67 CPU) @ 272702.48/s (n=1000000)
M1 = 0 3 6 10 15
M2 = 0 3 6 10 15
G = 0 3 6 10 15
Ashrunk = B C D E F G H I J K L M N

As shown by elapsed times, it's useless to try to implement a remove function using either grep or map defined indexes. Just grep-remove directly.

Before testing I was thinking "map1" would be the most efficient... I should more often rely on Benchmark I guess. ;-)

Answer 2

If you know the array index, you can delete() it. The difference between splice() and delete() is that delete() does not renumber the remaining elements of the array.