A binary search seems a good idea: have a look at: Search::Binary.

Update: Searching for 5000 "matches" in an array of 10000 headers took this program 3 seconds:

use Modern::Perl;

use Search::Binary;

#fake lists of headers and matches
my @headers = map {state $header; $header += int(rand(10)) + 1} (1 .. 
+10000);
my @matches = map {int(rand($headers[-1])+1)} (1 .. 5000);

my $min = 0;
my $max = @headers - 1;

my $read = sub {
    my ($handle, $val, $position) = @_;
    state $last_position;
    if ($position) {
        $last_position = $position;
        return $val <=> $headers[$position], $position;
    }
    else {
        $last_position++;
        return $val <=> $headers[$last_position], $last_position;
    }
};

my $start_time = time;
for my $match (@matches) {
    my $pos = binary_search($min, $max, $match, $read, undef, 10);
    $pos++ if $headers[$pos] == $match;
    say "$match is between $headers[$pos - 1] and $headers[$pos] (posi
+tion: $pos)";
}
say "That took me ", time - $start_time, " seconds.";

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CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: search array for closest lower and higher number from another array by CountZero
in thread search array for closest lower and higher number from another array by bigbot

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