Perl: Iterating through this funky array? - arrays

Question

I'm trying to iterate over a 2D array that is structured in this specific way. Whether or not this is a good way to structure the array is another question - I still need to be able to iterate over it (if it is possible).
#row1 = ( "Current Scan", "Last Month");
#row2 = ( "240", "0");
#row3 = ( "226", "209");
#row4 = ( "215", "207");
#array = (\#row1, \#row2, \#row3, \#row4);
print Dumper(#array);
printarray(#array);
Dumper gives me the following output:
$VAR1 = [
'Current Scan',
'Last Month'
];
$VAR2 = [
'240',
'0'
];
$VAR3 = [
'226',
'209'
];
$VAR4 = [
'215',
'207'
];
I've tried several for loops with no success. Each only prints the first row ($VAR1) and quits. Here is my most recent attempt:
sub printarray {
#array = shift;
$rowi = 0;
foreach my $row (#array) {
for (my $coli = 0; $coli <= #$row; $coli++) {
print "$array[$rowi][$coli]\n";
}
$rowi++;
}
}
I'm obviously overlooking something simple. What am I doing wrong? Thanks in advance!

Answer 1

If you want just print the array, try following code:
foreach my $row (#array) {
foreach my $elem (#$row) {
print $elem; ## print elements without separator
}
print "\n"; ## new line after row
}
If you need indexes for some purpose, here we go:
for(my $row_i = 0; $row_i < #array; $row_i++) {
for(my $column_i = 0; $column_i < #{ $array[$row_i] }; $column_i++) {
print $array[$row_i][$column_i];
}
}
The idea is that #array in scalar context returns number of elements in array. And #{ $array[$row_i] } is a little more tricky. It dereference array stored in $array[$row_i].
Update for subroutine:
In perl you can pass array by reference:
printarray(\#array); ## pass reference
sub printarray {
my $array_ref = shift; ## no copy created
foreach my $row (#$array_ref) { ## now we need to dereference
...
}
}
You can also pass a copy of array:
printarray(#array);
sub printarray {
my #array_copy = #_; ## store local copy of array
...
}
For more details take a look at How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}? manual page.
And please add use strict; at the begining of programm. It'll force you to declare all variables, but will save bunch of time if you type something incorrectly.

Answer 2

When you pass the array into the subroutine, you're essentially passing in eight scalars. Then, when you do
sub printarray {
#array = shift;
... you're popping off only the first element in the list. Try:
sub printarray {
#array = #_;

Answer 3

#!/usr/bin/perl
use warnings;
use strict;
my #row1 = ( "Current Scan", "Last Month");
my #row2 = ( "240", "0");
my #row3 = ( "226", "209");
my #row4 = ( "215", "207");
my #array = (\#row1, \#row2, \#row3, \#row4);
foreach my $row (#array) {
foreach my $value (#$row) {
print "$value\n";
}
}
This will print
Current Scan
Last Month
240
0
226
209
215
207
Not sure if that's what you wanted.

Answer 4

Yes, the problem is in the way you're passing the array to the subroutine. Perl flattens arrays in parameter lists. Basically, printarray(#array) is (in this example) equivalent to printarray($array[0], $array[1], $array[2], $array[3]). The shift at the beginning of printarray takes the first parameter and assigns it to #array. So no matter how big the array is, printarray only sees the first element.

Answer 5

Are you looking for something like this:
#!/usr/bin/perl
use warnings;
use strict;
use Algorithm::Loops 'MapCar';
my #row1 = ( "Current Scan", "Last Month");
my #row2 = ( "240", "0");
my #row3 = ( "226", "209");
my #row4 = ( "215", "207");
my #array = (\#row1, \#row2, \#row3, \#row4);
MapCar { print "Scan: $_[0]: $_[1], $_[2], $_[3]\n" } #array;