Perhaps this is fishing for you rather than teaching you to fish, but here's how I'd do it: 
#!/usr/bin/perl -w
use strict;
my %result;
for my $row(<DATA>) {
    my($num,$date,$time)=split /\s+/,$row;
    push @{ $result{$num}->{$date} }, $time;
}
for my $num(sort keys %result) {
    for my $date(sort keys %{$result{$num}}) {
        my %contains;
        my @time_ary;
        for my $time(sort @{$result{$num}->{$date}} ){
            push @time_ary, $time unless $contains{$time}++;
        }
        printf "%s\t%s\t%s\n", $num,$date,join(',',@time_ary);
    }
}
__DATA__
848    05/23/06    11:00
848    05/23/06    12:30
848    05/23/06    13:00
848    05/23/06    14:00
848    05/25/06    11:00
848    05/25/06    12:00
261    05/24/06    11:00
261    05/24/06    12:30
261    05/24/06    13:00
261    05/24/06    13:00
261    05/24/06    13:00
261    05/24/06    13:00

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In reply to Re: Combining flat file records by jZed
in thread Combining flat file records by pglinx

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