/home/ap0calypse

hi,

these days I was encountering a problem, when I was going through 2 veeeeeeery big hashes to find out which of them have similar keys (not really same keys, just slightly different). I thought, that the easiest way would be to go through both hashes in 2 for-loops and check them out one by one. Unfortunately, this approach took about 2 minutes to go through (2 minutes seem like an eternity if you are staring at a terminal).

My first approach looked like this:

for my $a (keys %b) {
    for my $c (keys %d) {
        if ($c =~ m/^$a.+$/) {
            print "bingo!\n";
        }
    }
}

You see, the keys in the second hash (%d) always look like the keys in the first hash (%b) with the only difference, that they contain the key plus some other stuff. So if $a looks like “abc”, $c looks like “abc123″. Now, if you have 2 hashes with – let’s say – 5000 keys and values, you can easily calculate how long this could take…. (5000 x 5000 = 25.000.000) … as I already said: it takes FOREVER!

Now, after some searching around I found a very nice solution on the Linux and Unix Forums from a guy called “pludi”. He recommended a grep-approach. Here is now my remodelled version:

for my $a (keys %b) {
    for my $c (grep { /^$a.+$/ } keys %d) {
        print "bingo!\n";
    }
}

Voila. Instead of taking 2 minutes, the loop now runs through in 15 seconds. I love Perl

ok, today I finished my work at the fancy little script I mentioned yesterday. You can download it now here. Because wordpress for some reason doesn’t allow me to upload files without a filename-extension (grrr) it now has a txt-ending. please just ignore the extension …..

you call the script like this:

$ ./oebbquery "Innsbruck Hbf" "Wörgl Hbf"
Connections from Innsbruck Hbf to Wörgl Hbf:
 
Departure  Arrival  Duration  Changes  Train(s)
15:13      15:59     0:46     0        rex 
15:28      16:24     0:56     0        s 
15:54      16:28     0:34     0        oec

Please be sure to use the correct names of the stations. for example: “wörgl” doesn’t work, but “Wörgl Hbf” works. You have to use the names provided by the oebb-website.

the output looks now like this:

have fun!