PerlMonks =),

I'm playing with an 'array of hashes of arrays' and having some problems with data manipulation and was wondering if there might be some incite from above to help out...


We have the following data structure,

List (array of things)
|->hash of data about things (name, inputs, outputs)
|->some data elements require arrays of data. (can have multiple inputs and outputs)

In the following code the AddConnection subroutine works fine and pushes the $from and $to variables into the arrays of the hash of object properties, which belongs to an array of objects. 
sub AddConnection {
        my ($from, $to) = @_;

        for $l ( @list ) {
                if ( $l->{"name"} eq $from ) {
                        push @{$l->{"outputs"}}, $to;
                }
                if ( $l->{"name"} eq $to ) {
                        push @{$l->{"inputs"}}, $from;
                }
        }


}

sub AddRandomConnection {
        my @arr;

        my $i = scalar(@inputlist);
        print "we have $i elements to choose from\n";
        my $rand_i = int(rand($i));
        my $from = $inputlist[$rand_i];
        print "we picked $rand_i : $from\n";

        my $o = scalar(@inputlist);
        print "we have $i elements to choose from\n";
        my $rand_o = int(rand($o));
        my $to = $outputlist[$rand_o];
        print "we picked $rand_o : $to\n";
        #TODO: need to make sure you can't come to and from same node

        for $l ( @list ) {
                if ( $l->{"name"} eq $from ) {
                        push @{$l->{"outputs"}}, $to;
                }
                if ( $l->{"name"} eq $to ) {
                        push @{$l->{"inputs"}}, $from;
                }
        }

}

[download]

The issue comes with the second function AddRandomConnection which employs the same code to access the data, but returns the following error upon execution.

we have 2 elements to choose from
we picked 0 : O1
we have 2 elements to choose from
we picked 1 : I2
Modification of a read-only value attempted at <myfile> line 73.

As can be seen the error message eludes to accessing bad data or some such, but the selection of elements 0 and 1 are within the limits of the array size of two for each element.
Can anyone see my oversight?

Regards Paul =)

Edit by castaway - Added readmore tags

In reply to Array of hashes of Arrays by thekestrel

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