File's absolute values after subtraction in perl - perl

Question

I have the below table (txt file with /t separator) and I want to write a script to subtract each time the values of the next line to the previous line and then to obtain the absolute value of each value.
43 402 51 360 66
61 63 67 66 65
63 60 69 63 58
65 53 89 55 57
103 138 135 135 85
For example:
abs(61-43) abs(63-402) abs(67-51) abs(66-360) abs(65-66)
abs(63-61) abs(60-63) abs(69-67) abs(63-66) abs(58-65) etc..
This is what I wrote.
#!/usr/bin/perl -w
use strict;
use warnings;
my $filename = '/home/kgee/Desktop/gene_gangs/table_gangs/table_ony_numbers';
open(my $fh, '<:encoding(UTF-8)', $filename)
or die "Could not open file '$filename' $!";
$newtable=0;
$i=0;
$j=1;
while (my $row = <$fh>) {
chomp $row;
print "$row\n";
my #numbertable = split//,$filename;
for (#numbertable){
$newtable[$j]= ($i+2) -($i+1);
$temp[$i]= abs($newtable[$j]);
$newtable=$tepm[$i];
my #newtable= split//,$newtable;
print("#newtable","\n");
$i=$i+1;
}
}
I got many errors all of them are "global symbol XXX requires explicit package name (did you forget to declare "my XXX"?) at line XXX?"
I read online that to step over this issue you have remove the use warnings;(from the begging) which is not recommanded or to declare the variable outside the block (and not inside!). I tried both but still I have some warnings.

Answer 1

OK first off: Do not "turn off warnings" ever. Would you turn off the warnings on your car, and expect that to end well? Warnings are there because there's something you need to fix, not ignore.
my is used to declare a variable the first time you use it.
This is as simple as
my $newtable = 0;
You've also added some routes of confusion into your code, and I'd suggest you sort:
Indent it properly
Don't use $newtable and #newtable - they're different variables, and it's way too easy to mix up $newtable; and $newtable[0];
You've got $temp and $tepm - this is exactly the sort of thing that use warnings helps you identify.
Splitting $filename to get #numbertable - I'm pretty sure that doesn't do what you you want, because it's splitting the string '/home/kgee/Desktop/gene_gangs/table_gangs/table_ony_numbers' into characters. Did you perhaps mean split /\t/, $row;?
Likewise my #newtable= split//,$newtable; ... I don't think that does what you think it does either, because $newtable is 'just' zero as instantiated earlier in your program, and you never modify it.
for (#numbertable) iterates each element in that table (the split row?) but you don't ever use the iterator. $_ is set to the current element each iteration. But it doesn't have anything to do with $i and $j, and you don't actually seem to modify $j at all - so it stays zero.
perl -w and use warnings; is redundant. You should probably stick with one or other. (I favour use warnings; along with use strict; personally).
Actually, the more I look at the code, I'm afraid it becomes clear it doesn't actually work, and your problems run a bit deeper than your initial warnings.
How about:
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my #previous_row;
my #new_table;
##iterate line by line - use your file handle here, <DATA> is a special case.
while ( <DATA> ) {
#strip trailing linefeed.
chomp;
#split this row on any whitespace (which includes tabs)
my #row = split;
#Handle first iteration - can't subtract 'previous row' if there isn't one.
if ( #previous_row ) {
my #new_row;
#iterate the current row
foreach my $element ( #row ) {
#grab the elements off the previous row - note "shift" modifies it, and this will
#break if you've got uneven length rows. (But you don't, and I'll leave it to you to handle that if you do.
my $previous_row_element = shift #previous_row;
#calculate new value
my $value = abs ( $element - $previous_row_element );
#stash new value into new row.
push #new_row, $value;
}
#new row is complete, so push it into the new table.
push #new_table, \#new_row;
}
#Update 'previous row' with the contents of the current row.
#previous_row = #row;
}
#lazy mode output. Iterating the array and printing values in the format you want
#is up to you.
print Dumper \#new_table;
__DATA__
43 402 51 360 66
61 63 67 66 65
63 60 69 63 58
65 53 89 55 57
103 138 135 135 85

Answer 2

See #Sobrique's answer for excellent explanation of some problems with your script. I just present an alternative approach here:
use feature qw(say);
use strict;
use warnings;
my $filename = 'table_only_numbers';
open(my $fh, '<:encoding(UTF-8)', $filename)
or die "Could not open file '$filename': $!";
my #row1;
while (my $row = <$fh>) {
chomp $row;
my #row2 = split " ", $row;
if (#row1) {
die "Bad format!" if #row1 != #row2;
my #new = map { abs ($row2[$_] - $row1[$_]) } 0..$#row2;
say join " ", #new;
}
#row1 = #row2;
}
close $fh;