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

In reply to Re: How do I parse and evaluate a file line-by-line? by Trimbach
in thread How do I parse and evaluate a file line-by-line? by kendroid

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