Do the numbers in the first column matter? They appear to be line numbers in the data file. Using them as array indexes will leave only the 4n+1 ones defined.

Assuming they don't matter, I notice that they are grouped so that the number divided by 4 is the same within a group. Therefore:

my @aryhash;
while (<HANDLE>) {
    chomp;
    my @dat = split " ", $_; # magical whitespace split
    $aryhash[$dat[0]/4|0]->{$dat[2]} = $dat[3];
}
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This is a pretty direct way to do it, but is tightly bound to your data format.

After Compline,
Zaxo