unable to parse different rows in array

rocketperl has asked for the wisdom of the Perl Monks concerning the following question:

Hi i have a tsv containing two columns. I have loaded the two columns in seperate rows. I want to subtract the 1st value in second column with the 2nd value in the first column and keep going on till the end of the file. When i try subtracting the 1st element in the second column with the 1st element 1st column it works perfectly fine. When i try to start with the index of 1,0 in array for subtraction, i get error as "use of uninitialized value". please help me i dont know how to figure out the correct assignment.

       while (<FILE>)
{
    chomp;
    ($first,$second)=split ("\t");
    my @first_column= split '\n',$first;
    my @second_column=split '\n',$second;
    my $a=0;
    my $b=0;
    print "$first_column[$a]";
    print "\t$second_column[$b]";
    my $e=$second_column[$b]-$first_column[$a];
    print "\t$e\n";
    
$a++;
$b++;

}
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Re: unable to parse different rows in array by hdb (Monsignor) on Jul 01, 2013 at 09:36 UTC
You do not seem to understand the comments you receive in your earlier threads. Re-posting will not get you much in the Monastery. Here is a list of your troubles: `$first` and `$second` do not seem to be declared with `my`. `@firstcolumn` and `@secondcolumn` need to exist during the whole loop and but are being re-instantiated in each iteration. They need to be declared before the loop. `<FILE>` reads your file until and including a newline, `chomp` removes that newline, so `$_` contains no newline. And therefore `$first` and `$second` do not contain any newlines, splitting on newlines makes no sense. `$a` and `$b` are also re-declared in every iteration of the loop, so their value from previous lines is forgotten every time you read a new line from the file. This is not all but should get you started.	[reply] [d/l] [select]
Re: unable to parse different rows in array by marto (Cardinal) on Jul 01, 2013 at 09:34 UTC
I suggest you read the advice given in your previous thread (unable to parse different rows in array), and all of your other questions. There's a pattern you're either ignoring or not seeing. Read and adviuce you've been given, and how to debug these problems you keep having.	[reply]
Re: unable to parse different rows in array by Laurent_R (Canon) on Jul 01, 2013 at 17:47 UTC
In addition to what has already been said, if you have a tsv i.e., I assume, tab separated values), then you probably want to split on \t rather than \n.	[reply]