Re: Idiomatic Perl for GPA Calculation

[Alfred Vahau]

Thank you for the pointer. I will check the calculation again for GPA of 
1.98 against id 216.
Clearly there is no problem for allowed grades so 1.40 has been 
confirmed for 386.

Alfred,
Ankur Gupta wrote:
----
#!/usr/bin/perl
# This is the GPA calculation routine for the
# Eduadmin system again.
#
$ifile = 'gpa.dat';
open (INF, "<$ifile") || die "Can't open file $ifile:$!\n";
$cp_total = 0;
$id = 0;
$temp = 0;
LINE:  while (<INF>) {                     ($id, $grade, $cp) = 
split;                   if ($grade =~ /NG/i       ||
              $grade =~ /YL/i       ||
              $grade =~ /DF/i       ||
              $grade =~ /\bY\b/i    ||
              $grade =~ /W/i        ||
              $grade =~ /T/i)     {next LINE;}

              $cp_total += 
$cp;                                                      if ($grade 
=~ /\bA\b/i) {                      $a6++ if $cp == 
6;                                        $a4++ if $cp == 
4;                                        $a3++ if $cp == 
3;                                        $a2++ if $cp == 
2;                                              }
            if ($grade =~ /\bB\b/i) {                      $b6++ if 
$cp == 6;                                        $b4++ if $cp == 
4;                                        $b3++ if $cp == 
3;                                        $b2++ if $cp == 
2;                                              }

       if ($grade =~ /\bC\b/i) {                      $c6++ if $cp == 
6;                                        $c4++ if $cp == 
4;                                        $c3++ if $cp == 
3;                                        $c2++ if $cp == 
2;                                              }

       if ($grade =~ /\bD\b/i) {                      $d6++ if $cp == 
6;                                        $d4++ if $cp == 
4;                                        $d3++ if $cp == 
3;                                        $d2++ if $cp == 
2;                                              }

      if ($temp == $id) {
         next LINE;
       }
      else {
        $wcp = ($a6*4.0*6.0 + $a4*4.0*4.0 + $a3*4.0*3.0 + $a2*4.0*2.0) +
               ($b6*3.0*6.0 + $b4*3.0*4.0 + $b3*3.0*3.0 + $b2*3.0*2.0) +
               ($c6*2.0*6.0 + $c4*2.0*4.0 + $c3*2.0*3.0 + $c2*2.0*2.0) +
               ($d6*1.0*6.0 + $d4*1.0*4.0 + $d3*1.0*3.0 + $d2*1.0*2.0);
                            $gpa = $wcp / $cp_total;
           $temp = $id;
           $cp_total = 0;
           next LINE;
      }
} # end of while
use hashes of hashes.........
#Lets first store the hashes
while(<INF>){
   ($id, $grade, $cp) = split(/\s+/);
   #I am removing the .00 for convenience. You can preserve it and 
make changes accordingly
   $cp =~ s/(\d)\.00/$1/;
   #No need for label.. lets put everything in one search
   next if  $grade =~ /(NG|YL|DF|\bY\b|W|T)/ ;
   #This is the best part.. I am creating hashes of hashes of hashes. 
The hashes takes care of uniqueness.
   $student{$id}->{$grade}->{$cp}++;
   #Simple hash for sum of credit points
   $cp_total{$id} += $cp;
}

#Now calculate the weighted credit points for each student..
foreach $id ( keys %student ){
   #Even this can be improved by using more foreaches. But lets keep 
it like this for easy readability
   $wcp = ($student{$id}->{A}->{6}*24 + $student{$id}->{A}->{4}*16 + 
$student{$id}->{A}->{3}*12 + $student{$id}->{A}->{2}*8)+
                ($student{$id}->{B}->{6}*18 + 
$student{$id}->{B}->{4}*12 + $student{$id}->{B}->{3}*9 + 
$student{$id}->{B}->{2}*6)+
                ($student{$id}->{C}->{6}*12 + 
$student{$id}->{C}->{4}*8 + $student{$id}->{C}->{3}*6 + 
$student{$id}->{C}->{2}*6)+
                ($student{$id}->{D}->{6}*6 + $student{$id}->{D}->{4}*4 
+ $student{$id}->{D}->{3}*3 + $student{$id}->{D}->{2}*2);
   #Calculate the gpa and store it for each student
   $gpa{$id} = $wcp/$cp_total{$id};
}

#Lets print it now. We could have done it in the above foreach also ..
foreach $id (keys %student){
   print "GPA for $id : $gpa{$id}\n";
}
BTW, I got these values
GPA for 216 : 1.98
GPA for 386 : 1.40
Although it is correct for 386.. it does not matches for id 216. Are 
you sure gpa for 216 is correct.

Hope you got the idea of how you can use hashes to make the program 
short and simple.

--
Ankur

--
Perl - 
"... making the easy jobs easy,
without making the hard jobs impossible."
'The Camel', 3ed

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