Sekhar Reddy:

Using code tags (<c>Your code goes here</c>) would be far better than trying to manually format your code:

• It preserves spaces, so people can see your indentation
• It's far easier than manually inserting all those paragraph tags
• It's less error-prone as you don't have to manually look for <, > (et. al.) and patch them up.
• It lets the site offer a "download" button to let people more easily grab your code

If you had used code tags, it would look more like the following:

use Data::Dumper;

my %results = ();
while ( <DATA> ) {
    chomp;
    my @row = split /,/, $_;
    print STDOUT "row values is:".$_."\n";
    if ( (exists $results{ $row[0], $row[1] })) {
        if ( ( $row[2] ) <
                $results{ $row[0], $row[1] }->{ 'ACTDATE' }
        ) {
            $results{ $row[0],$row[1] }->{ 'ACTDATE' } = $row[2] ;
        }
        print STDOUT "inactdate--".$row[3]." \n";
        print STDOUT "in memory inact--".$results{ $row[0] }->{ 'INACT
+DATE' }."\n";
        if ( ( defined $row[3]) && !( defined $results{ $row[0] }->{ '
+INACTDATE' } )
        ) {
            $results{ $row[0] }->{ 'INACTDATE' } = undef ;
        }
[download]

Obviously not exactly like that, as I don't know how your code is normally formatted, nor did I bother to clean up the whole thing.

OK, for the errors you're encountering: I'd suggest you start looking at how you're accessing the data items you're putting in results. You're storing some items into the hash like this:

    $results{ $row[0], $row[1] } = {
        'A1' => $row[0],
        'B1' => $row[1],
        'ACTDATE' => $row[2],
        'INACTDATE' => $row[3],
    }
[download]

but you're sometimes referring to them like:

but at other times you're doing things like:

I expect the mismatched hash keys are the reason that you're getting all the "uninitialized value warnings. Clean that up and that will probably get you closer to your desired result.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

The code you posted is (with some minor changes).

Split the line into 4 named variables instead of @row (makes the problem clearer).

Eliminate quoting keys to the hash when they exist of all word characters (so don't need to be quoted).

#!/usr/bin/perl
use strict;
use warnings;

my %results;
open my $fh, '<', 'file1.csv' or die $!;

while ( <$fh> ) {
    chomp ;
    my ($a1, $b1, $actDt, $inactDt) = split /,/;
    
    if (exists $results{$a1,$b1} ) {
    
        if ($actDt < $results{$a1,$b1}{ACTDATE}) {
            $results{$a1,$b1}{ACTDATE} = $actDt;
        }
            
        if (!$inactDt || !$results{$a1,$b1}{INACTDATE}) {
            $results{$a1,$b1}{INACTDATE} = '' ;
        }
        elsif($inactDt > $results{$a1,$b1}{INACTDATE} ) {
            $results{$a1,$b1}{INACTDATE} = $inactDt;
        }
    }
    else {  
        # Create new entry in hash
        $results{$a1,$b1} = {
            A1 => $a1,
            B1 => $b1,
            ACTDATE => $actDt,
            INACTDATE => $inactDt,
        };
    }
}
    
foreach ( sort keys %results ) {
    my $a1 = $results{ $_ }{A1} ;
    my $b1 = $results{ $_ }{B1} ;
    my $actDt = $results{ $_ }{ACTDATE};
    my $inactDt = $results{ $_ }{INACTDATE};
    print "$a1,$b1,$actDt,$inactDt\n" ;
}
[download]

7900724655,200906888,20180416,20180830
7900724655,200906889,20180601,20180728
7900724655,200906890,20180905,
7900724666,200906868,20180416,20180830
7900724666,200906869,20180601,20180728
7900724666,200906890,20180905,
[download]

To get the results you want doesn't require a hash.

#!/usr/bin/perl
use strict;
use warnings;

open my $fh, '<', 'file1.csv' or die $!;

my ($actDt, $inactDt, $count) = ('', '', 0);
my $previous_key = '';

while (<$fh>) {
    chomp;
    my ($a1, $b1, $begin, $end) = split /,/;
    my $key = "$a1,$b1";
    
    if ($previous_key eq $key) {
        $inactDt = $end;
        $count++;
    }
    else { # either reached the end of a record or this is the first r
+ecord
        print join(",", $previous_key, $actDt, $inactDt), "\n"
            if $count > 1;
        $actDt = $begin;
        $inactDt = $end;
        $count = 1;
    }
    $previous_key = $key;
}

print join(",", $previous_key, $actDt, $inactDt), "\n"
    if $count > 1;
[download]

7900724655,200906889,20180601,20180728
7900724655,200906890,20180905,
7900724666,200906869,20180601,20180728
7900724666,200906890,20180905,
[download]

7900724655,200906888,20180416,20180522
7900724655,200906889,20180601,20180720
7900724655,200906889,20180724,20180728
7900724655,200906888,20180730,20180830
7900724655,200906890,20180905,20180930
7900724655,200906890,20181005,20181030
7900724655,200906890,20181104,
7900724666,200906868,20180416,20180522
7900724666,200906869,20180601,20180720
7900724666,200906869,20180724,20180728
7900724666,200906868,20180730,20180830
7900724666,200906890,20180905,20180930
7900724666,200906890,20181005,20181030
7900724666,200906890,20181104,
[download]

Hi Athanasius,

First of all thank you very much for your try. I tried with your code, but still that is also giving some incorrect results. Below fyi.

Input data that i have considered below

7900724666,200906888,20180416,20180522
7900724666,200906888,20180601,20180720
7900724666,200906888,20180406,20180411
7900724677,200906872,20180301,20180330
7900724677,200906871,20180101,20180228
7900724677,200906873,20180401,20180420
7900724688,200906881,20180101,20180228
7900724688,200906881,20180303,20180330
7900724688,200906882,20180404,20180430
7900724688,200906883,20180508,20180620
7900724699,200906891,20180101,20180228
7900724699,200906891,20180303,20180330
7900724699,200906892,20180404,20180430
7900724699,200906893,20180508,
7900724611,200906888,20180416,20180522
7900724611,200906889,20180724,20180728
7900724611,200906889,20180601,20180720
7900724611,200906888,20180730,20180830
7900724611,200906890,20180905,20180930
7900724611,200906890,20181005,20181030
7900724611,200906890,20181104,
7900724622,200906868,20180416,20180522
7900724622,200906869,20180601,20180720
7900724622,200906869,20180724,20180728
7900724622,200906868,20180730,20180830
7900724622,200906890,20180905,20180930
7900724622,200906890,20181005,20181030
7900724622,200906890,20181104,
[download]

The output which i have got is below

7900724666,200906888,20180416,20180411
7900724688,200906881,20180101,20180330
7900724699,200906891,20180101,20180330
7900724611,200906889,20180724,20180720
7900724611,200906890,20180905,
7900724622,200906869,20180601,20180728
7900724622,200906890,20180905,
[download]

Here 1st line and 4th line in output are incorrect: Ex:

7900724611,200906889,20180724,20180720
[download]

Here expected result in output 4th line is 7900724611,200906889,20180601,20180728