Looping through double arrays

[LuckyKoen]

I have some trouble with showing data in an array. I have 2 arrays and I put one array in another :

my @array1;
my @arraygroup
push (@array1, "a");
push (@array1, "b");
push (@arraygroup, @array1);

This seems to be no problem for perl, when I use the following loop I get " ab " as a result :

foreach my $array (in $arraygroup) {
print $array;
}

I want to address each item in array1 separately though, so I try the following :

foreach my $array (in $arraygroup) {
print $array[0];
}

Which doesn't work since I defined $array instead of @array, so I change this :

foreach my @array (in $arraygroup) {
print $array[0];
}

This won't work either because foreach requires a $variable to be declared and won't take an array instead. How should I get this thing to work ?

Also, are there better alternatives to double arrays in Perl ? I use these often in Java but I haven't found much about them in Perl yet. I'm wondering why they aren't that common.

 

[tchatzi]

I didn't understand what is it that you want to do but i 'll give you some hints

If you set things like you did

my @array1;
my @arraygroup[red];[/red]  #you forgot the ';'
push (@array1, "a");
push (@array1, "b");
push (@arraygroup, @array1);

then you have 

$array1[0] = "a"
$array1[1] = "b"
$arraygroup[0] = "a"
$arraygroup[1] = "b"

so if you want to print them just say 

print $array1[0];
print $arraygroup[1];
.....

if you want to just go through them do it like this

foreach (@array1){
   print $_,"\n";    #which gives you 'a' and on the next line 'b'
}

or 

foreach my $element (@arraygroup){
   print $element;
}

such thing as 
[red]foreach my @array (in $arraygroup) {
    print $array[0];
}[/red] [b]does not exists[/b]

if you want you can do something like this

my @array = @arraygroup;

and then 

print $array[0];  #which gives 'a'

or 

foreach (@array){
   print $_,"\n";
}

``The wise man doesn't give the right answers,
he poses the right questions.''
TIMTOWTDI

 

[ishnid]

Technically, an array can't contain another array as one of its elements, so pushing @array1 into @arraygroup isn't going to do what you want it to. It is, however, perfectly valid syntax, which is why it won't give you an error, though I won't go into that right now.

Array elements can only be scalars. However, a reference to an array is a perfectly legitimate scalar to hold in an array. Thus, to get @array1 into @arraygroup is like this (the backslash is the `reference of' operator):

push (@arraygroup, \@array1);

Now, you can loop through @arraygroup like any other array (Note: there's no `in' operator in Perl):

foreach my $element ( @arraygroup ) {
   # do something
}

Now for the `do something' bit! - normally, to access the first element of an array @array, you'd do this: $array[0]. However, when you have a reference to an array, rather than an actual array, you need to dereference using the `->' operator, i.e.:

foreach my $element ( @arraygroup ) {
   print $element->[0];
}

That will now print the first element in each array contained in @arraygroup. To print every element in every array, do this:

foreach my $outer_element( @arraygroup ) {
   foreach my $inner_element( @{ $outer_element } ) {
      print $inner_element;
   }
}

Note that now we use @{ ..arrayref.. } to convert an array reference into an array.

To read more on complex data structures in perl, google for `perllol'.

Hope some of that makes sense!

 

[LuckyKoen]

Thanks Ish, that answer couldn't have been more clear