I am looking to add an array to a csv file as a column. I basically have to csv files containing a column of numbers. There csv files have 100,000's of lines. Example:

Time1 
1  
2  
3  
 
Time 2
4
5
6
[download]

What I want to do is take columns from 2 different csv files, subtract the 2nd from the 1st and then add a new column to the 2nd file with a column called difference and the result. So far, I have got as far as creating an array with the difference in it. I am having trouble to actually put this array back as a column into the 2nd file. Does anyone have any suggestions. I want to keep the code I've written thus far if possible though. I was able to add the array of values to the end of the csv file but not after each line.

use 5.10.0; 

use warnings;




my $output = "results.txt";
my ($fh1, $fh2, $fh3, $fh4, $fh5);
my ($file1, $file2) = @ARGV;
my (@col1, @col2, @col3);
my ($lines, $lines2, $lines3);
my (@array, @array2) = ();
my @diff = ();

my $csv = "csv.csv";

###Open files for read and write###
open ($fh1, '<', $file1) or die $!;
open ($fh2, '+<', $file2) or die $!;
open ($fh3, '>', $output) or die $!;


#open my $out, ">", "out.csv" or die $!;

###Reads lines from file into an array###
      while ($lines = <$fh1>){
      chomp $lines;#Removes the new line
      @col = split "," , $lines; #Array where each index holds the dat
+a of each column
      push @array, $col[5]; #adding element to the array containing sl
+ack values for file
      }

shift @array;#Removes the header line from the array -i.e column name

###Reads lines from file into an array###
      while ($lines2 = <$fh2>){
      print $fh4 $lines2;
      chomp $lines2;
      #push @list, $lines2;
      @col2 = split "," , $lines2;
      push @arr, @col2;
      push @array2, $col2[5];

      
      }

shift @array2;

###Iterates through the array and finds the difference in slack###
      foreach  my $i (@array){
    $diffs  = $array2[$i] - $array[$i];#Variable showing difference
    push @diff, $diffs;#Adding element to an array containing the diff
+erence values
      }  
###Prints out the 2 differenct slacks from each run and shows the diff
+erence between them.

#print $fh3 "Difference :", $array[$_] ,"-", $array2[$_], " = ", $diff
+[$_], "\n" for 1 .. $#array;
unshift @diff, "Difference";
[download]

2018-07-14 Athanasius fixed closing code tag and added code tags around data

---

In reply to Adding an array to an existing csv file as a new column by c.con

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.