Something that comes up fairly often is a need to split a string to equal sized chunks. For instance, given the string "abcdefgh12345678", splitting it to 4-char chunks would produce ("abcd", "efgh", "1234", "5678"). Looking around the monastery, there're at least a couple of posts I have found.

I tried to time some different techniques against each other:

my $str = "abcdefgh12345678" x 20;
my $strlen = length $str;


cmpthese(50000, {

'grep_split' => sub 
{
  my @arr = grep {$_} split /(.{8})/, $str;
},

'split_pos' => sub
{
  my @arr = split /(?(?{pos() % 8})(?!))/, $str;
},

'substr_map' => sub
{
    my $len = length $str;
  my @arr = map {substr($str, $_ * 8, 8)} (0 .. $strlen / 8 - 1);
},

'substr_loop' => sub
{
  my @arr;
  my $len = length $str;
  for (my $i = 0; $i < $len; $i += 8)
  {
    push(@arr, substr($str, $i, 8));
  }
},

'unpack' => sub 
{
  my @arr = unpack('(A8)*', $str);
}
});

[download]

And the results are quite surprising: 

               Rate   
split_pos    3203/s
grep_split   6425/s
substr_map   8889/s
unpack      11348/s
substr_loop 15097/s

[download]

Contrary to what I have expected from my understanding (that built in functions should be faster than loops), the looping solution is the swiftest. It beats the unpack by a margin ranging from 15 to 50 percent, depending on the length of the string and the chunks.

Any way to make it faster ?

In reply to Splitting a string to chunks by spurperl

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