Hi, I'd suggest you build a hash keyed by name and then a sub-hash per name keyed by the date, with the values stored in an array. (To lovers of acronyms this would be a HOHOA (hash of hashes of arrays)).

use strict; use warnings;
use feature 'say';

my %result;

for my $line (<DATA>) {
    chomp $line;
    my ( $name, $date, $val ) = split ' ', $line;
    push @{ $result{ $name }{ $date } }, $val;
}

for my $name ( keys %result ) {
    say $name;
    for my $date ( keys %{ $result{ $name } } ) {
        say "\t$date: @{ $result{ $name }{ $date } }";
    }
}

__DATA__
nick 20/5/1950 one
john 18/2/1980 two
nick 19/6/1978 three
nick 20/5/1950 four
nick 12/9/2000 five
john 15/6/1997 six
nick 20/5/1950 seven
[download]

$ perl 1221691.pl

john
    15/6/1997: six
    18/2/1980: two
nick
    19/6/1978: three
    20/5/1950: one four seven
    12/9/2000: five
[download]

Hope this helps!

and that would be a HoTHel !

edit: he said tab-separated so '\t' probably?

Here's one way: If there is a character that you know doesn't occur in either the name or the date (like a tab), you can use that to separate the two and make a single hash key out of it. Note that in the sample data that you've posted here, you don't have any tabs, so I've had to guess that all of your columns are separated by tabs. However, in that case, my ( $name, $rest ) = split /\t/; is only grabbing the first two columns. Also, you probably want to chomp your lines.

use strict;
use warnings;

my %res;
while (<DATA>) {
    chomp;
    my ( $name, $date, @rest ) = split /\t/;
    push @{ $res{"$name\t$date"} }, @rest;
}
for my $key ( sort keys %res ) {
    my ( $name, $date ) = split /\t/, $key, 2;
    print "$name,$date:", join( "|", @{ $res{$key} } ), "\n";
}

__DATA__
nick    20/5/1950    one
john    18/2/1980    two    two and a half
nick    19/6/1978    three
nick    20/5/1950    four
nick    12/9/2000    five
john    15/6/1997    six
nick    20/5/1950    seven    eight
[download]

Output:

john,15/6/1997:six
john,18/2/1980:two|two and a half
nick,12/9/2000:five
nick,19/6/1978:three
nick,20/5/1950:one|four|seven|eight
[download]

In the above code, using \t to separate the hash key is safe, because of the split /\t/ I know that none of the strings will contain tabs. If you choose a separator character of which you're not sure if it's contained in the strings, like say |, you may want to add a check like die $name if $name=~/\|/; die $date if $date=~/\|/; to play it safe. Also, you can use a separator that is very unlikely to appear, like $/ or \0 (but again, if you want to code defensively, check for its presence anyway). (Update: $/ is the input record separator, which chomp removes for you. Also made minor fix to the latter two regexes.)

Update 2: I should also mention that using a module like Text::CSV is generally better for reading this kind of data, because it handles things like quoted fields and escaped characters for you (also install Text::CSV_XS for speed).

There is a built-in mechanism for this: see perldoc -v '$;'.

Interesting approach, thank you!

I see that you have already received good replies. Here is another way to perform this task. The Data::Table module has many useful methods for manipulating tabular data. In this case, the group method is applicable.

The data.tsv file contains the following tab-delimited data

nick    20/5/1950    one
john    18/2/1980    two
nick    19/6/1978    three
nick    20/5/1950    four
nick    12/9/2000    five
john    15/6/1997    six
nick    20/5/1950    seven
[download]

#!/usr/bin/env perl

use strict;
use warnings;

use Data::Table;

# Load input data from tsv file
#   The first argument is the file name
#   The second argument specifies that there is no header row (in this
+ case
#   the Data::Table object that is created will have auto-generated co
+lumn
#   names of col1, col2, etc.
my $dt = Data::Table::fromTSV('data.tsv', 0);

print "The input table is:\n";
print $dt->tsv, "\n\n";

# Group by 'col1' and 'col2'
my $output_t = $dt->group(
    ['col1', 'col2'], # columns to group by
    ['col3'], # Columns to perform calculation on
    [ \&join_vals ], # Apply join_vals function to values found in 'co
+l3' 
    ['values'] # Put the joined values into these columns 
);

print "The output table is:\n";
print $output_t->tsv, "\n\n";

sub join_vals {
  my @data = @_;
  return join("|", @data);
}

exit;
[download]

The input table is:
col1    col2    col3
nick    20/5/1950    one
john    18/2/1980    two
nick    19/6/1978    three
nick    20/5/1950    four
nick    12/9/2000    five
john    15/6/1997    six
nick    20/5/1950    seven


The output table is:
col1    col2    values
nick    20/5/1950    one|four|seven
john    18/2/1980    two
nick    19/6/1978    three
nick    12/9/2000    five
john    15/6/1997    six
[download]

The standard solution for handling files containing character-separated values (CSV), including tabulator separated values, is to use Text::CSV and - if possible - its accelerating companion Text::CSV_XS. It is "the standard" because it not only splits (and joins) on the separating character(s), but also handles quoting, escaping, and all of those nasty edge cases you can find in CSV files.

If you are used to work with relational databases and DBI, try DBD::CSV. It sits on top of Text::CSV and allows you to treat CSV files like database tables in a relational database. In other words: You can use SQL to work directly with CSV files.

All of those modules are currently maintained by our helpful Tux.

Alexander