Passing interior array of two-dimensional array to subroutine

[johntology]

Hello,

I've made a two dimensional array using references, which I gather is the only way to do it in Perl. I now need to pass each interior array to a subroutine for processing and can't quite work out the syntax. Here's what I have so far. As you can see, my understanding of Perl falls apart when I get to the subroutine. Any help would make my day. Thanks.

my @fruitFiles =("apple.html", "orange.html", "kiwi.html");
my @vegetableFiles =("pea.html", "carrot.html", "limabean.html"); 
my @breadFiles =("rye.html", "wheat.html", "sevenGrain.html"); 
 
 
#Make references to arrays.
my $fruitArray = \@fruitFiles; 
my $vegArray = \@vegetableFiles;
my $breadArray = \@breadFiles;
 
 
# Put references into an array to make a two-dimensional array.
@categoryArrays = ($fruitArray, $vegArray, $breadArray);
 
#Proof of concept, debug.
for my $i (0..$#categoryArrays) {
   for my $j (0..$#{$categoryArrays[$i]}) {            
      print "\$i = $i, \$j = $j, $categoryArrays[$i][$j]\n";
   }
}
 
 
for my $q (0..$#categoryArrays) {
    #pass each array to subroutine.
   &buildList ($categoryArrays[$q]);  
   }
 
 
sub buildList($catArray)
{
@locArray = $catArray;
foreach $element (@locArray)
{
print $element;
print "\n";
# I actually want to open all of the files in the passed array, manipulate and concatenate bits of them into an output file.
# I think I can manage that part if I can just reference them correctly down here.
}
 
}
 
 

[Ganon11]

Hello,

I've made a two dimensional array using references, which I gather is the only way to do it in Perl. I now need to pass each interior array to a subroutine for processing and can't quite work out the syntax. Here's what I have so far. As you can see, my understanding of Perl falls apart when I get to the subroutine. Any help would make my day. Thanks.

#Make references to arrays.
my $fruitArray = \@fruitFiles; 
my $vegArray = \@vegetableFiles;
my $breadArray = \@breadFiles;
 
 
# Put references into an array to make a two-dimensional array.
@categoryArrays = ($fruitArray, $vegArray, $breadArray);
 
for my $q (0..$#categoryArrays) {
    #pass each array to subroutine.
   &buildList ($categoryArrays[$q]);  
   }
 
 
sub buildList($catArray)
{
@locArray = $catArray;
foreach $element (@locArray)
{
print $element;
print "\n";
# I actually want to open all of the files in the passed array, manipulate and concatenate bits of them into an output file.
# I think I can manage that part if I can just reference them correctly down here.
}
 
}
 
 

All right, so inside buildList, we assume that you were passed in a reference to an array. (I'm not sure what the parentheses syntax is you've used - I haven't come across that in my studies). So @_ (the array with all of the arguments passed to the current subroutine) should have 1 element - the reference. You want locArray to be the array that is referenced - I can see that, because you use a foreach loop to access all members. But what you have now:

@locArray = $catArray;

means @locArray will be an array with 1 element - the reference you were passed in. If you want to get the array, you need to dereference the reference:

@locArray = @{$catArray};

Now @locArray is an array with the same contents as the array referenced by $catArray.

As an aside, why aren't you using my to declare these variables as lexicals? i.e. shouldn't it be:

sub buildList($catArray)
{
   # I think this should actually be:
# sub buildList
# {
#    my @locArray = @{$_[0]};
   my @locArray = @{$catArray};
   foreach my $element (@locArray)
   {
      print $element;
      print "\n";
   }
 
}

You might have perfectly good reasons for doing so that I don't understand (after all, I'm taking my first class in Perl right now, so I don't have a lot of experience).

[KevinADC]

I did not go over all the code, but change the buildList function to this:

sub buildList
{
my $locArray = shift; # imports the data into the function 
foreach $element (@{$locArray})
{
print $element;
print "\n";
# I actually want to open all of the files in the passed array, manipulate and concatenate bits of them into an output file.
# I think I can manage that part if I can just reference them correctly down here.
}
 
}

Ask questions if you have any.

[johntology]

Thank you both! Kevin, yours worked well; Gannon, thanks for the tips and thoughtful walk-through. I never took coursework in Perl so I have gaping holes in my knowledge and, I forget e.g., about "my".
Can either of you tell me how in the subroutine I can retrieve the name of the array variable I passed in? I need to be able to refer to the literal, "fruitArray".
Thanks.
John

[Ganon11]

You could add its name to the front of the actual array, or pass it into the subroutine as an additional variable. Otherwise, there is no way - remember that a variable's name is only for us programmers to comprehend and has nothing to do with the actual value that gets passed around.

[KevinADC]

Thank you both! Kevin, yours worked well; Gannon, thanks for the tips and thoughtful walk-through. I never took coursework in Perl so I have gaping holes in my knowledge and, I forget e.g., about "my".
Can either of you tell me how in the subroutine I can retrieve the name of the array variable I passed in? I need to be able to refer to the literal, "fruitArray".
Thanks.
John

You need to rethink your premise, there should never be a need to retrieve an array name in a perl program. You could pass it as a string to your function as Ganon11 suggests.

[johntology]

Gotcha. Thank you both again.

John