Reference two dimensional array in Perl sub

photon · #1 (**permalink**) 04-14-2003

I am trying to reference a two dimensional array in a
subroutine and can't seem to figure this one out in Perl.

Does anybody know? Please enlighten me.

Code:

#!/usr/bin/perl -w

use constant DIM => 4;

sub Shift_elements_right{
    my (@Input, @Output) = @_;
    for ($i = 0 ; $i <= DIM ; $i++ ){
	$Output[$i + 1] = $Input[$i];
    }
    $Output[1] = $Input[DIM];
}


# Initialize
for ($i = 0; $i <= DIM; $i++){
    $weight[0][$i] = $i;
}

# Shift call
for ($i = 0; $i <= DIM; $i++){
    Shift_elements_right(\@weight[$i], \@weight[$i + 1]);
}

# Print output.
for ($i = 0; $i <= DIM; $i++){
    for ($j = 0; $j <= DIM; $j++){
	print "Weight $i : $weight[$i][$j]\t";
    }
    print "\n";
}

oombera · #2 (**permalink**) 04-15-2003

Could you explain a little more about what you're trying to do?

I can pick out some of what you're doing, but I'm not sure why.. if you explain the what and why of your situation, it'll help us help you out..

photon · #3 (**permalink**) 04-15-2003

This is actually a more complex Pascal program I
am converting to Perl. The code given is a smaller
example of a larger program.

In pascal the program code looks like this:

Code:

CONST DIM = 4;
TYPE Vector = ARRAY [1..DIM] of REAL;
weights: ARRAY[1..DIM] of Vector;

PROCEDURE Initialize;
	VAR I: INTEGER;

	BEGIN
	FOR I := 1 TO DIM DO
		weights[1][I] := I;
	END



PROCEDURE Shift_elements_right (Input : Vector;
				VAR Output: Vector);
	VAR I: INTEGER;
	
	BEGIN
	FOR I := 1 TO DIM DO
		Output[I+1] := Input[I];
	Ouptut[1] := Input[DIM];
	END

BEGIN
FOR I := 1 TO DIM DO
	Shift_elements_right(weights[I], weights[I+1]);
END;

It is supposed to create a 4 x 4 dimensional array with only
the first row of vector being initialized.

My question is to reproduce this in Perl. I would like to
pass the array as a reference and put values in the 4 x 4
dimentional array through a subroutine.

Odviously I can do this without a subroutine but with a
larger program this is not practicle.

oombera · #4 (**permalink**) 04-15-2003

To initialize the two-dimensional array, you could do something like:

Code:

@array1 = ('0', '0', '0', '0');
@array2 = ('0', '0', '0', '0');
@array3 = ('0', '0', '0', '0');
@array4 = ('0', '0', '0', '0');

@bigArray = (\@array1, \@array2, \@array3, \@array4);

or to simplify, try this (I think it'll work):

Code:

@bigArray = ( ['0', '0', '0', '0'],
              ['0', '0', '0', '0'],
              ['0', '0', '0', '0'],
              ['0', '0', '0', '0']
);

Then to reference a particular value, you can use:

Code:

$bigArray[0][0]; # first row, first column
$bigArray[2][1]; # third row, second column

To store a value, use:

Code:

$bigArray[2][1] = '5'

or, in a subroutine:

Code:

for ($i = 0; $i < DIM; $i++){
    for ($j = 0; $j < DIM; $j++){
        bigArray[$i][$j] = $j; #assuming $j is the value you want to store...
    }
}

Let me know what works and what doesn't...

photon · #5 (**permalink**) 04-15-2003

The following code seems to solve my problem.

Code:

#!/usr/bin/perl -w

use constant DIM => 4;

sub Shift_elements_right{
    my ($ref) = shift;
    for($j = 1 ; $j <= DIM ; $j++){
	for ($i = 1 ; $i <= DIM ; $i++ ){
	    $ref->[$j + 1][$i + 1] = $ref->[$j][$i];
	}
    $ref->[$j + 1][1] = $ref->[$j][DIM];
    }
}


# Initialize
for ($i = 1; $i <= DIM; $i++){
	$weights[1][$i] = $i;
}

# Shift call
Shift_elements_right(\@weights);

# Print output.
for ($i = 1; $i <= DIM; $i++){
    for ($j = 1; $j <= DIM; $j++){
	print "Weight $i : $weights[$i][$j]\t";
    }
    print "\n";
}

WIntellect · #6 (**permalink**) 04-16-2003

Quote:

snip of sample code
FOR I := 1 TO DIM DO
weights[1][I] := I;
END

If you want to keep your Perl code similar to the original, I believe you can do things like the above, in this way:

Quote:

foreach $I (1..DIM) {
# process $I here
}

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