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10. Data-Processing: Grade Book Example

This example produces a score summary report by combining data from a simple file of student info and a file of their scores.

Input file "stufile" is delimited with colons. Fields are Student ID, Name, Year:

    123456:Washington,George:SR
    246802:Lincoln,Abraham "Abe":SO
    357913:Jefferson,Thomas:JR
    212121:Roosevelt,Theodore "Teddy":SO

Input file "scorefile" is delimited with blanks. Fields are Student ID, Exam number, Score on exam. Note that Abe is missing exam 2:

    123456 1 98
    212121 1 86
    246802 1 89
    357913 1 90
    123456 2 96
    212121 2 88
    357913 2 92
    123456 3 97
    212121 3 96
    246802 3 95
    357913 3 94

The desired report:

    Stu-ID Name...                       1   2   3   Totals:

    357913 Jefferson,Thomas             90  92  94       276
    246802 Lincoln,Abraham "Abe"        89      95       184
    212121 Roosevelt,Theodore "Teddy"   86  88  96       270
    123456 Washington,George            98  96  97       291

                              Totals:  363 276 382

The program that made this report:

    #!/usr/local/bin/perl
    # Gradebook - demonstrates I/O, associative
    # arrays, sorting, and report formatting.
    # This accommodates any number of exams and students
    # and missing data.  Input files are:
    $stufile='stufile';
    $scorefile='scorefile';

    # If file opens successfully, this evaluates as "true", and Perl
    # does not evaluate rest of the "or" "||"
    open (NAMES,"<$stufile")
        || die "Can't open $stufile $!";
    open (SCORES,"<$scorefile")
        || die "Can't open $scorefile $!";

    # Build an associative array of student info
    # keyed by student number

    while (<NAMES>) {
            ($stuid,$name,$year) = split(':',$_);
            $name{$stuid}=$name;
            if (length($name)>$maxnamelength) {
                    $maxnamelength=length($name);
            }
    }
    close NAMES;

    # Build a table from the test scores:

    while (<SCORES>) {
       ($stuid,$examno,$score) = split;
       $score{$stuid,$examno} = $score;
       if ($examno > $maxexamno) {
          $maxexamno = $examno;
       }
    }
    close SCORES;

    # Print the report from accumulated data!

    printf "%6s %-${maxnamelength}s ",
            'Stu-ID','Name...';
    foreach $examno (1..$maxexamno) {
            printf "%4d",$examno;
    }
    printf "%10s\n\n",'Totals:';

    # Subroutine "byname" is used to sort the %name array.
    # The "sort" function gives variables $a and $b to
    # subroutines it calls.
    # "x cmp y" function returns -1 if x<y, 0 if x=y,
    # +1 if x>y.  See the Perl documentation for details.

    sub byname { $name{$a} cmp $name{$b} }

    # Order student IDs so the names appear alphabetically:
    foreach $stuid ( sort byname keys(%name) ) {
       # Print scores for a student, and a total:
       printf "%6d %-${maxnamelength}s ",
               $stuid,$name{$stuid};
       $total = 0;
          foreach $examno (1..$maxexamno) {
             printf "%4s",$score{$stuid,$examno};
             $total += $score{$stuid,$examno};
             $examtot{$examno} += $score{$stuid,$examno};
          }
          printf "%10d\n",$total;
    }

    printf "\n%6s %${maxnamelength}s ",'',"Totals: ";
    foreach $examno (1..$maxexamno) {
       printf "%4d",$examtot{$examno};
    }
    print "\n";
    exit(0);

Perl allows an associative array to be "tied" to a genuine database, such that expressions like $record = $student{$key} use the database. See the "dbm" and "tie" functions.