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Add successive entries

mgpg
Novice

Mar 12, 2008, 12:25 PM

Post #1 of 2 (1621 views)

Add successive entries	Can't Post

Hi, I have the following input:

A,1
A,4
A,2
B,3
B,0
C,23
...

I want to simply output A, SUM(all A entries). I already sorted this file so all A's are successive. I can write simple perl script to do this as follows:

Code

  $prev; 
  $sum = 0; 
  $line =~ /(\w+),(\d+)/; $cur = $1; $n = $2; 
  if ($cur == $prev) { $sum += $n;} 
  else { print "$prev, $sum\n"; $sum = $n; } 
  $prev = $cur; 
  # loop

This is probably not the most efficient but something like this will work I think. I wonder if I can write a one-liner from command line to do this.

Thanks.

KevinR
Veteran

Mar 13, 2008, 12:22 AM

Post #2 of 2 (1614 views)

Re: [mgpg] Add successive entries [In reply to]	Can't Post

Use a hash. Assuming the file is sorted with all A entries first:

Code

my %hash; 
open (IN, 'file') or die "$!"; 
while(<IN>){ 
   my ($k,$v) = split(/,/); 
   last if ($k ne 'A'); 
   $hash{$k}+=$v; 
} 
close IN; 
print "A = $hash{A}";

If all you wanted were the A lines you could grep the file to get only the A lines then apply the above code. It probably could be done with a one liner too. I will leave that up to you.
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