in reply to Matching First Character of Strings Efficiently

Trade a little setup time for speed in the loop and use a hash? 

my @list = ...;
my %list; @list{ map{ substr $_, 0, 1 } @list } = ();

my $str_a = 'Foo';                               
my $first_c = substr $str_a, 0, 1;
for my $str_b ( @list ) {                         
    next if exists $list{ $first_char };  
    expensive_function($str_a , $str_b);
}

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Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail

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Re: Re: Matching First Character of Strings Efficiently
by Limbic~Region (Chancellor) on Mar 15, 2004 at 20:16 UTC
    BrowserUk,
    I am very interested to see if this solution has an efficiency breakpoint. It certainly would not be as memory efficient as some of the other solutions, but that was not a requirement - just speed.

    Cheers - L~R

[reply]

      Sorry Limbic~Region, I got carried away with your "Only modify this line" (and had a brainfart too!).

      There is no point in looping over the array, that's why we put in a hash. It should have looked something like this. 

      my @list = ...;
my %list; @list{ map{ substr $_, 0, 1 } @list } = ();

my $str_a = 'Foo';                               
expensive_function($str_a , $str_b) 
    unless exists $list{ substr $str_a, 0, 1 };

      [download]
      Examine what is said, not who speaks.
      "Efficiency is intelligent laziness." -David Dunham
      "Think for yourself!" - Abigail
[reply]
[d/l]
        BrowserUk,
        Actually, unless I am missing something I can't include this solution at all. The testing to see if the two strings first characters are the same is just the initial test. The expensive_function actually does a futher comparison. I had a brain fart to when reading it.

        Cheers - L~R

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