Your script gets much much simpler by putting your data in a database and then using standard SQL to retrieve the data. When working with data and manipulating the data in various ways, always think "database"!

For example:

use Modern::Perl '2014';
use DBI;

my $dbfile = 'c:/data/school.sqlite';
my $dbh =
  DBI->connect( "dbi:SQLite:dbname=$dbfile", "", "", { RaiseError => 1
+ } );

my $sth = $dbh->prepare('INSERT INTO students (id, name) VALUES (?, ?)
+');
while (<DATA>) {
    chomp;
    last if /grades.txt/;
    next unless $_;
    next if /^\*\*\*/;
    say $_;
    my ( $id, $name ) = split /:/;
    $sth->execute( $id, $name );
}

$sth =
  $dbh->prepare('INSERT INTO results (id, course, score) VALUES (?, ?,
+ ?)');
while (<DATA>) {
    chomp;
    next unless $_;
    next if /^\*\*\*/;
    my ( $id, $course, $score ) = split /\s+/;
    $sth->execute( $id, $course, $score );
}

my $ary_ref = $dbh->selectall_arrayref(
'SELECT name, sum(score), avg(score), min(score), max(score) FROM resu
+lts JOIN students WHERE students.id = results.id GROUP BY results.id 
+ORDER BY name'
);

printf "%20s %10s %8s %8s %8s\n", qw/Name Total Average Min Max/;
for my $line (@$ary_ref) {
    printf "%20s %10d %8d %8d %8d\n", @$line;
}

$ary_ref = $dbh->selectall_arrayref(
    'SELECT course, avg(score) FROM results GROUP BY course ORDER BY c
+ourse');

printf "\n%10s %8s\n", qw/Course Average/;
for my $line (@$ary_ref) {
    printf "%10d %8d\n", @$line;
}

__DATA__

***students.txt***
122334:James,Lebron:
222223:Duncan,Tim:
244668:Bryant,Kobe:
355779:Durant,Kevin:
******************

***grades.txt***
122334 1 98
222223 1 86
...(snip)...
244668 5 95
355779 5 94
****************
[download]

Output:

                Name      Total  Average      Min      Max
         Bryant,Kobe        466       93       89       95
          Duncan,Tim        462       92       86       96
        Durant,Kevin        468       93       90       96
        James,Lebron        485       97       96       98

    Course  Average
         1       90
         2       93
         3       95
         4       95
         5       95
[download]

Retrieving data is just one line of Perl-code and since the data is saved in the database you can use it again and again without running the cost of parsing the input file(s).

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.