Re: How do I parse and evaluate a file line-by-line?

Here's one quick solution:

#!/usr/bin/perl -w

use strict;
my $last = "";
my $cursor = -1;
my @output;

while (<DATA>) {
    my ($time, $switch) = split "\t";
    if ($switch eq $last) {
        $output[$cursor] = $_;
    } else {
       $cursor++;
       $output[$cursor] = $_;
       $last = $switch;
    }
}

foreach (@output) {
    print;
}


__DATA__
time1    UP
time2    DOWN
time3    UP
time4    DOWN
time5    DOWN
time6    DOWN
time7    UP
time8    UP
time9    UP
time10    DOWN
time11    UP
[download]

The idea here is to record just the last "UP" or "DOWN" event in a string of one or more "UP" or "DOWN" events. $cursor is used to keep our place in the array, overwritting successive UP's and DOWN's as necessary.

Gary Blackburn
Trained Killer

Comment on Re: How do I parse and evaluate a file line-by-line? Download Code

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Re: Re: How do I parse and evaluate a file line-by-line? by merlyn (Sage) on Mar 03, 2001 at 20:47 UTC
You can tighten that middle loop up a bit by getting out of "C think" and getting into "Perl think": `while (<DATA>) { my ($time, $switch) = split "\t"; if ($switch eq $last) { $output[-1] = $_; } else { push @output, $_; $last = $switch; } }` [download] The $cursor variable is unnecessary, because Perl always knows how long the array is. -- Randal L. Schwartz, Perl hacker	[reply] [d/l]
Re: Re: Re: How do I parse and evaluate a file line-by-line? by Trimbach (Curate) on Mar 03, 2001 at 20:57 UTC
Thanks for that... I rarely use `$array[$element]` to grow an array, preferring "push", but I couldn't use push indiscriminately here because I needed to write over successive instances of UP or DOWN. Of course, `$array[-1]` was exactly what I was looking for. Gotta get used to using the relative position in an array.... And for the record, it wasn't "C think" as I actually know absolutely nothing about C. It was just inexperience. :-D Gary Blackburn Trained Killer	[reply] [d/l] [select]