Is this close to what you're describing?

#! perl -slw
use strict;

my @data;
$data[ $_ ] = [ map int( rand 100 ), 1 .. 10 ] for 0 .. 1e3;

my @lookback;
my $matches = 0;
for my $row ( @data ) {
    for my $lb ( @lookback ) {
        if( $row->[ 3 ] < 10  && $lb->[ 7 ] > 50 ) {
            print "condition matched ", ++$matches;
            last;
        }
    }

    push @lookback, $row;
    shift @lookback if @lookback > 15;
}
[download]

It might be, but my Perl knowledge isn't up to the level at which I could understand that code :)
Dyslexics Untie !!!

It is not complicated code. Take it one line at a time and study it.

Play with it. Add print statements to see what is going on. Ask questions -- in this thread -- about things you do not understand.

With a few hours or a coupe of days you should be able to make sense of it. And that time will stand you in good stead for the rest of your Perl experience.

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

An illustration to see whether I understand your problem: I create an array of array refs with 5 lines (instead of your 15 to keep it small) and 11 columns (0 to 10) called @lookback. Then I extract column number 3 (the fourth column) from this AoA, result called @column. Is that the right direction?

use strict;
use warnings;
use Data::Dumper;

my @lookback;
for my $line (1..5) {
    push @lookback, [ map { "$line.$_" } 0..10 ]; 
}

print Dumper \@lookback;

my $col = 3;
my @column = map { $_->[$col] } @lookback;

print Dumper \@column;
[download]

It's close, but I'm copying the rows into the look-back array. I don't see why it should make a difference, but it does.

I can read the any selected field from the original array of arrays, but when I copy the rows into the look-back array I can't access any field in those rows.

Should I be copyng references to those rows instead of copying the rows themselves ?
Dyslexics Untie !!!

Why do I have a feeling that the more I read about your problems, the more you should tell us the entire problem you are trying to solve instead of just a small portion of it, and how you have coded that small portion? i.e. why do you have an array of arrays, why do you need to look back over 15 rows, why does the data you are looking for change etc.

The small portion of it is the problem - that's where I'm getting stuck with error message. The rest of the script is working.

The reason I have to look back over the previous 15 rows is not relevant to the array problem. It's a requirement of the processing, nothing more.

The data value that I'm looking for changes because it's based on the several values in the current row of original data (which has 17 fields). Deriving that value is not an issue, the code produces the correct value to search for.
Dyslexics Untie !!!

That seems the simplest way to me but with 2 counters say $ix,$n. [$ix] for current position and $n counting from 1 to 15 pointing to previous row [$ix-$n] in turn. You will need to adjust the logic for the first 15 records of course.

I'm reluctantly coming to the conclusion that I'll have to abandon the look-back array concept. Apparently, two-dimensional arrays in Perl are too difficult to actually use for someone at my level :(

I'll need at least three counters, though. The original array has data for up to a full year, and I have to start the comparison search over with each new day. So I'd need an overall original array counter, and the other two counters would reset when the day turns over.

Dyslexics Untie !!!