Advanced Perl Programming

Pass the Envelope

Let us say we are given a text file containing Academy Award (Oscar) winners by year and category, formatted as follows:

1995:Actor:Nicholas Cage
1995:Picture:Braveheart
1995:Supporting Actor:Kevin Spacey
1994:Actor:Tom Hanks
1994:Picture:Forrest Gump
1928:Picture:WINGS

We would like to provide the following services:^[16]

• Given a year and category, print the corresponding entry.

• Given a year, print all entries for that year.

• Given a category, print the year and title of all entries for that category.

• Print all entries sorted by category or by year.

Data Representation

Since we would like to retrieve entries by category or by year, we use a double indexing scheme, as shown in Figure 2.2.

Figure 2-2. Data structure to represent Oscar winners

Each entry includes a category, a year, and the name of the corresponding winner. We choose to keep this information in an anonymous array (an anonymous hash would do just as well). The two indices %year_index and %category_index map the year and category to anonymous arrays containing references to the entries. Here is one way to build this structure:

open (F, "oscar.txt") || die "Could not open database: $!"; %category_index = (); %year_index = (); while ($line = <F>) { chomp $line; ($year, $category, $name) = split (/:/, $line); create_entry($year, $category, $name) if $name; } sub create_entry { # create_entry (year, category, name) ...