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Why isn't a 2D array printed in Perl printing?

Handling 2D arrays in Perl is giving me a headache. Anyway, next question:

I have a loop that pushes an array like @twoOneArray into another array, say @twoDimArray, and then reset to the next iteration of the loop, and then reinserted into @twoDimArray with a new set of values, When I print this @twoDimArray using :

print Dumper \@twoDimArray;

he outputs

OUTPUT

$VAR1 = [

      [

        'BB',

        'AA',

        'AA'
       ],
       $VAR1->[0],
       $VAR1->[0],
       $VAR1->[0]
     ];

or using loops

for (my $i=0; $i<4; $i++){
    for (my $j=0; $j<4; $j++){
         print "$twoDimArray[$i][$j] \n";
    }
}

data is duplicated.

OUTPUT

Row = 0 BB AA AA

Row = 1 BB AA AA

Row = 2 BB AA AA

Row = 3 BB AA AA

etc....

I can't figure out why both exit paths go wrong. If I print @twoDimArray every time (before going to the next iteration of the loop, i.e. after using the push function) the @twoOneArray is inserted, then the values ​​seem to be accurate and not repeated, but printing in one pass seems to give above mistake. A similar question was asked here , but I'm not sure if this makes sense to me. Any suggestions?

Code to build 2D array:

for ($k = 1; $k <= $counter; $k++){
        @twoOneArray = (); #reset it when loop starts again
        for ($j = 0; $j <= $colsInArray; $j++){
        #do stuff to create @twoOneDim
        }
        push @twoDimArray, \@twoOneArray;
        #if I print @twoDimArray if prints fine, with the exact values intact
}

print Dumper \@twoDimArray; #if I print it here it messes up
print "\n";
0


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4 answers


The Data :: Dumper output tells me that your problem isn't printing the array. Data: Damper never lies (or only rarely).

Please show us the code that you used to build the array. I'm sure there is a bug in this code somewhere.

UPDATE:



Now that you've added the code that creates the array, I can see that you've fallen into an evil trap: you're adding a @twoOneArray reference to your "outer" array. But the link will always be the same every time through your loop. Change your code like this:

for ($k = 1; $k <= $counter; $k++){
        my @twoOneArray; # REALLY reset it when loop starts again
        for ($j = 0; $j <= $colsInArray; $j++){
            #do stuff to create @twoOneDim
        }
        push @twoDimArray, \@twoOneArray;
}

.. and it should work.

+10


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You did something like this:

@a = (1, 2, 3);
push @b, \@a;

@a = (2, 3, 4);
push @b, \@a;

# ...

The problem is that you click @b

on the link to @a

. All links point to the same @a

. Data::Dumper

tells you what's $VAR->[0]

wrong with his thing.

You need to do something like:



$a = [ 1, 2, 3 ];
push @b, $a;

$a = [ 2, 3, 4] ;
push @b, $a;

# ....

So the [ ... ]

arrayref syntax will create a new reference array every time.

I suggest you read perlreftut and perlref carefully.

edit: I see that you posted your code and, yes, you do my code with code. Change your syntax usage [ ... ]

and you should be fine.

+4


source


Your question has been satisfied by others. I would add that the inference from Data::Dumper

is useful in identifying problems like this: [1]

your array element is being dumped as $VAR1->[0]

- in other words, it is a reference to the same underlying data values ​​stored in [0]

.

+4


source


If you want an array of arrays then you should push references to arrays like

my @a = qw(1 2 3 4 5 6 7 8);
my @b = qw(a b c d e f g h);
my @aOfa;

push(@aOfa, \@a);
push(@aOfa, \@b);
-3


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