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Re: How do I get the Nth Character of a String?

by PetaMem (Priest)
on Sep 14, 2009 at 13:42 UTC ( #795133=note: print w/replies, xml ) Need Help??


in reply to How do I get the Nth Character of a String?

split is slow. However, if you want just the first character of the string (I often do), then you can significantly speed up split by giving it the value 2 as LIMIT argument.

Benchmarked code from above (obviously on a faster machine) with 1 million iterations:

split: 17 wallclock secs (16.69 usr + 0.02 sys = 16.71 CPU) @ 59 +844.40/s (n=1000000) substr: 0 wallclock secs ( 0.74 usr + 0.00 sys = 0.74 CPU) @ 13 +51351.35/s (n=1000000) unpack: 1 wallclock secs ( 1.02 usr + 0.00 sys = 1.02 CPU) @ 98 +0392.16/s (n=1000000)
Benchmarking a very similar code, but instead looking for the 1st char only and giving split a ,2 limit:
split: 2 wallclock secs ( 1.16 usr + 0.00 sys = 1.16 CPU) @ 86 +2068.97/s (n=1000000) substr: 1 wallclock secs ( 0.70 usr + 0.00 sys = 0.70 CPU) @ 14 +28571.43/s (n=1000000) unpack: 0 wallclock secs ( 0.96 usr + 0.00 sys = 0.96 CPU) @ 10 +41666.67/s (n=1000000)
#!/usr/bin/perl -w use strict; use Benchmark; use vars qw/$str/; $str = "123456789asgdjlaskjglkajblnlbnlaqjteoijqotijwojgl;akjglkj"; timethese(shift || 1000000, { 'unpack' => sub { my $char = getn_unpack($str, 1) }, 'substr' => sub { my $char = getn_substr($str, 1) }, 'split' => sub { my $char = getn_split($str, 1) } }); sub getn_unpack { return unpack "x" . ($_[1]-1) . "a", $_[0]; } sub getn_substr { return substr $_[0], $_[1]-1, 1; } sub getn_split { return +(split //, $_[0],2)[$_[1]-1]; }

Still slower than the other solutions, but nevertheless a speedup of over 10 to an unrestricted split. See if using the LIMIT argument in split would help your code.

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