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Re: nondestructive way to look at a character in a string

by kcott (Bishop)
on Jan 16, 2022 at 11:02 UTC ( #11140500=note: print w/replies, xml ) Need Help??

in reply to nondestructive way to look at a character in a string

G'day BernieC,

I would have used index for this (rather than the previously suggested substr).

With index, you are doing exactly what you show in your spec: is the character at a certain position the one you want. With substr, you are extracting a character at a certain position, and then performing a comparison operation.

The amount of coding for both is the same:

$ perl -E ' my @x = qw{ABC DEF BXB}; my ($i, $c) = qw{1 B}; for (@x) { say "$_: ", $i == index($_, $c, $i) ? "YES" : "NO"; say "$_: ", $c eq substr($_, $i, 1) ? "YES" : "NO"; } ' ABC: YES ABC: YES DEF: NO DEF: NO BXB: NO BXB: NO

A Benchmark indicated that index was roughly twice as fast as substr. I used much the same code as I showed above:

#!/usr/bin/env perl use strict; use warnings; use Benchmark 'cmpthese'; my @x = qw{ABC DEF BXB}; my ($i, $c) = qw{1 B}; cmpthese 0 => { index => sub { $i == index($_, $c, $i) ? 1 : 0 for @x }, substr => sub { $c eq substr($_, $i, 1) ? 1 : 0 for @x }, };

I ran this three times. All results were very close. The middle was:

Rate substr index substr 3981142/s -- -46% index 7383385/s 85% --

— Ken

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