Re: Matching First Character of Strings Efficiently

substr is usually pretty fast:

my $str_a = 'Foo';
my $letter = substr $str_a, 0, 1;
for my $str_b ( @list ) {
    next if $letter eq substr $str_b, 0, 1;
    expensive_function($str_a , $str_b);
}
[download]

-Mark

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Re: Re: Matching First Character of Strings Efficiently by bageler (Hermit) on Mar 15, 2004 at 20:38 UTC
why not combine the two commands in the loop? `my $str_a = 'Foo'; my $letter = substr $str_a, 0, 1; for my $str_b ( @list ) { unless ($letter eq substr $str_b,0,1) { expensive_function($str_a +, $str_b); } }` [download] update: unless eq is going to be slightly better than if ne	[reply] [d/l]
Re:x3 Matching First Character of Strings Efficiently by grinder (Bishop) on Mar 15, 2004 at 22:24 UTC
Well, if this is in a tight loop, then you might gain a bit by not building a scope each time through the loop: `expensive_function($str_a , $str_b) unless ($letter eq substr $str_b,0 +,1);` [download] IOW, get rid of the curlies. I'd be curious to find out if this really has any significant effect... Or even... `expensive_function($str_a , $_) unless ($letter eq substr $_,0,1) for @list;` [download] ... if we are free to play with $_ (otherwise predeclaring $str_b will work too).	[reply] [d/l] [select]