BernieC has asked for the wisdom of the Perl Monks concerning the following question:

I *must* be missing something. I want to do a simple check: 
if ({nthcharacter of $string} eq "x")

[download]
and I can't figure out how to do it. My inclination was to use splice, but splice *removes* the character from the string, so splice($string, n, 1) just won't do. I could do 
my @b = split(//, $string) ;
if ($b[n] eq "x") {...}

[download]
but that seems really klunky. Am I missing some simple/elegant way to do this?

Replies are listed 'Best First'.
Re: nondestructive way to look at a character in a string
by kcott (Archbishop) on Jan 16, 2022 at 11:02 UTC

    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

    [download]

    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 },
};

    [download]

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

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

    [download]

    — Ken

[reply]
[d/l]
[select]
Re: nondestructive way to look at a character in a string
by Anonymous Monk on Jan 15, 2022 at 20:06 UTC
[reply]
      Of course. It slipped my mind and when I was flailing around trying to remember it I ran across: 
      D:\>perldoc -f substr
No Perl script found in input

      [download]
      And I see my problem now -- for *some* reason, "perldoc -f" does not work from a command prompt when it is in the root of D:. That's for *anything: nothing works from D:. What a crazy thing -- I've tried it cd'ed to a dozen other directories on various other filesystems and it works perfectly.. but not from d:. oh well, now that I see what I did wrong. thanks for reminding my fuzzy mind {and prodding me to realize that perldoc wasn't working in this odd way}
[reply]
[d/l]

        It's available online at perldoc.perl.org. To wit, substr.

        [doh, this was basically indicated already. I'm being distracted.]

[reply]
[reply]
[d/l]

Back to Seekers of Perl Wisdom