How to read and print the common elements of multiple array in perl?

Question

I have stored values in 5 text files. The values in each text file should be considered as an array. I am trying to write a perl program, to read and print the common elements in these 5 arrays.

For Instance

@a1=(1,7,4,5); 

@a2=(1,9,4,5); 

@a3=qw(1,6,4,5 ); 

@a4=qw(1 2 4 5 ); 

@a5=qw(1 2 4 5 );

I expect to print

1 4 5

There is no question in this post, and you are expected to have tried your best and reached a barrier before you ask for help here. StackOverflow is not a free software agency. If you want advice on how to read the files you must explain what format they have. — Borodin
– Borodin, Commented Jul 26, 2012 at 8:58
I am a biology student, i never experienced with programming, i am learning perl myself. — CHE
– CHE, Commented Jul 26, 2012 at 9:03
read documentation about print function, about open function and <> operator (it is in IO-handling chapter) — gaussblurinc
– gaussblurinc, Commented Jul 26, 2012 at 9:05

Dave Cross · Accepted Answer · 2012-07-26 10:02:39Z

1

The perlfaq has lots of answer to questions that are frequently asked. Of course it's all a bit of a waste of time and effort if no-one bothers to check there before asking the question again :-)

How do I compute the difference of two arrays? How do I compute the intersection of two arrays?

Use a hash. Here's code to do both and more. It assumes that each element is unique in a given array:
my (@union, @intersection, @difference);
my %count = ();
foreach my $element (@array1, @array2) { $count{$element}++ }
foreach my $element (keys %count) {
    push @union, $element;
    push @{ $count{$element} > 1 ? \@intersection : \@difference }, $element;
}

You need the intersection of two arrays. And then do it three more times.

answered Jul 26, 2012 at 10:02

Dave Cross

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Comments

Borodin · Accepted Answer · 2012-07-26 12:23:29Z

1

You don't say what format your input files have, but this program will find all digit strings in each file and list the values common to all of them.

The list of input files is expected as command-line arguments.

use strict;
use warnings;

use File::Slurp 'read_file';

my %counts;

for (@ARGV) {
  $counts{$_}++ for map /\d+/g, read_file $_;
}

my @common = grep $counts{$_} == @ARGV, keys %counts;

printf "(%s)\n", join ', ', @common;

output

(4, 1, 5)

edited Jul 26, 2012 at 12:23

answered Jul 26, 2012 at 8:54

Borodin

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6 Comments

Borodin Over a year ago

@loldop: because I don't have agree with you or do what you tell me to

gaussblurinc Over a year ago

your comment to his question (with 3 vote up's) doesn't correlate with your answer.

gaussblurinc Over a year ago

you answer him, only that. as i see there is no information about format in question. you said that and make general-solution answer.

Borodin Over a year ago

@loldop: since there is a general solution that is likely to work I gave it. I said he shouldn't ask questions like that, not that I shouldn't answer them. How is it a problem for you?

gaussblurinc Over a year ago

as he said: biologist and learning perl by myself i think, that this is not he want. Explanation about IO-handling is better in this situation.

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