Comparing values in 2 textfiles and returning the missing values

[Jorgen Gustafsson]

Hi,
im trying to write a small progam to compare data in 2 textfiles.

I want to search for values that doesnt exist in File2.
The result should be "3" in the example below but Im not
able to do this since my program crosschecks all numbers in
both files and Im getting a lot of "hits". (outer and inner while-loops)


Below is an examples of the textfiles:

File1.txt File2.txt
1 1
2 2
3 4
4 5
5 6
7
8
9
10

Thanks in advance...!
Jorgen

 

[Jim Gibson]

Hi,
im trying to write a small progam to compare data in 2 textfiles.

I want to search for values that doesnt exist in File2.
The result should be "3" in the example below but Im not
able to do this since my program crosschecks all numbers in
both files and Im getting a lot of "hits". (outer and inner while-loops)


Below is an examples of the textfiles:

File1.txt File2.txt
1 1
2 2
3 4
4 5
5 6
7
8
9
10

Thanks in advance...!
Jorgen

If you have a program written, it is best to include that in your post.

If your files are short enough, you can try reading file 2 first and
creating a hash with the values from file 2 as keys (the value of the
hash doesn't matter, so set it to 1 or increment to get a count). Then,
read file 1 and see if the corresponding keys exist in your hash.

Here's a quick sample program (with two files appended and separated by
a BREAK line):

#!/opt/perl/bin/perl

use strict;
use warnings;

my %seen;
while(<DATA>) {
chomp;
last if /BREAK/;
$seen{$_}++;
}

while(<DATA>) {
chomp;
if( ! $seen{$_} ) {
print "$_ not in file 1\n";
}
}

__DATA__
1
2
4
5
6
7
8
9
10
BREAK
1
2
3
4
5

__OUTPUT__
3 not in file 1

FYI: This newsgroup is defunct. Try comp.lang.perl.misc in the future
for better response.

 

[Jürgen Exner]

Hi,
im trying to write a small progam to compare data in 2 textfiles.
I want to search for values that doesnt exist in File2.

perldoc -q difference:
"How do I compute the difference of two arrays? How do I compute the
intersection of two arrays?"

While the solution is written for arrays, it is trivial to modify it for
files.

jue

 

[Eric J. Roode]

Hi,
im trying to write a small progam to compare data in 2 textfiles.

I want to search for values that doesnt exist in File2.
The result should be "3" in the example below but Im not
able to do this since my program crosschecks all numbers in
both files and Im getting a lot of "hits". (outer and inner while-loops)

If you're on a unix-like system, you can use the 'comm' utility for this.

 

[Jorgen Gustafsson]

Hi, thanks for all help!

Found a link to a perl-module that seems to do the job for me in comp.lang.perl.misc.
(diff and sdiff)
http://search.cpan.org/~nedkonz/Algorithm-Diff-1.15/lib/Algorithm/Diff.pm#diff

/Jorgen