Transposing an array of elements - perl

Question

I am trying to transpose an array.
I tried the following code...
#! /usr/bin/perl
use strict;
use warnings;
use autodie;
open my $fh, '<',"op.txt" || die "$!";
open my $wh , '>',"pwl.txt" || die "$!";
select ($wh);
while (my $line = <$fh>) {
my #rows = $line;
my #transposed;
for my $row (#rows) {
for my $column (0 .. $#{$row}) {
push(#{$transposed[$column]}, $row->[$column]);
}
}
for my $new_row (#transposed) {
for my $new_col (#{$new_row}) {
print $new_col, " ";
}
print "\n";
}
}
**********INPUT FILE******
1 2 3
4 5 6
7 8 9
********** EXPECTED OUTPUT FILE *******
1 4 7
2 5 8
3 6 9
******** GENERATED OUTPUT FILE *******
Currently couldn't able print anything. script shows the error
"can't use string ("1 4 7") as an array ref while "strict refs" in use
Reference:
used the following reference...
Transpose in perl
however in this reference example, array input lines are declared manually where as i am trying to process a array which is in a text file
could anybody help me where i did mistake?
Many Thanks

Answer 1

You did have to split input line as #dland suggested. But, there were a few other issues.
Here's the corrected code [please pardon the gratuitous style cleanup]:
#! /usr/bin/perl
use strict;
use warnings;
use autodie;
open my $fh, '<',"op.txt" || die "$!";
open my $wh , '>',"pwl.txt" || die "$!";
my #rows;
while (my $line = <$fh>) {
my #line = split(" ",$line);
push(#rows,\#line);
}
close($fh);
my #transposed;
for my $row (#rows) {
push(#transposed,[]);
}
my $rowidx = -1;
for my $rowptr (#rows) {
++$rowidx;
my $colidx = -1;
for my $rowval (#$rowptr) {
++$colidx;
###printf("R=%d C=%d\n",$rowidx,$colidx);
my $colptr = $transposed[$colidx];
$colptr->[$rowidx] = $rowval;
}
}
for my $new_row (#transposed) {
for my $new_col (#$new_row) {
print $wh $new_col, " ";
}
print $wh "\n";
}
close($wh);
Note: It's slightly harder to transpose a non-square matrix. The above code may need to be extended a bit for that.

Answer 2

You're trying to shove a scalar into an array:
my #row = $line;
I think what you really want is to split on spaces:
my #row = split / /, $line;

Answer 3

adding my #row =map [ split], $line to my initial code is helping to print the data to pwl.txt.
however its not printing side by side.. instead it is printing to new line.
I guess because of this Mr.Borodin didn't include matrix in side while loop!
1
2
3
4
5
6
7
8
9

Answer 4

Here's a simpler way of doing this. It assumes all the rows are of the same length, and that all the lines in the file contain data -- i.e. there are no blank lines
The name of the input file is expected as a parameter on the command line, and the output is sent to STDOUT so it can be redirected on the command line. For instance
perl transpose.pl op.txt > pwl.txt
use strict;
use warnings 'all';
my #matrix = map [ split ], <>;
print "#$_\n" for #matrix;
print "\n";
my #transpose;
for my $i ( 0 .. $#{ $matrix[0] } ) {
$transpose[$i] = [ map { $_->[$i] } #matrix ]
}
print "#$_\n" for #transpose;
print "\n";
output
1 2 3
4 5 6
7 8 9
1 4 7
2 5 8
3 6 9