Loop through multidimensional Hash of Arrays in Perl - arrays

Question

I have a multidimensional hash of arrays that represent a student's grade in each subject for the first four assignments.
my %students_grades = (
Colton => {
English => [ 90, 95, 80, 75 ],
Mathematics => [ 77, 89,94, 100 ],
},
);
The syntax is a bit off but here's the code that creates the hash of arrays above.
#!/usr/bin/perl
my %students_grades;
$students_grades{'Colton'}{'English'}[0] = 90;
$students_grades{'Colton'}{'English'}[1] = 95;
$students_grades{'Colton'}{'English'}[2] = 80;
$students_grades{'Colton'}{'English'}[3] = 75;
$students_grades{'Colton'}{'History'}[0] = 77;
$students_grades{'Colton'}{'History'}[1] = 89;
$students_grades{'Colton'}{'History'}[2] = 94;
$students_grades{'Colton'}{'History'}[3] = 100;
How do I loop through the student's grades he received in History using a foreach loop? Right now I'm looping through it using a for loop.
my $num_of_grades = scalar #{$students_grades{'Colton'}{'History'}};
for (my $i=0; $i <= $num_of_grades; $i++) {
print $students_grades{'Colton'}{'History'}[$i] . "\n";
}
This is a representation of my code but in my actual program my hash of arrays is more complicated so I want to loop through the hash of arrays using a foreach loop because it'll be easier to handle. How do I do that?

Answer 1

for (my $i=0; $i<#array; ++$i) {
my $ele = $array[$i];
...
}
can be written simply as
for my $ele (#array) {
...
}
so you could have used the following:
for my $grade (#{ $students_grades{'Colton'}{'English'} }) {
print("$grade\n");
}
my $grade = $students_grades{'Colton'}{'English'}[0];
is short for
my $grade = $students_grades{'Colton'}->{'English'}->[0];
which means you can do
my $grades = $students_grades{'Colton'}{'English'};
my $grade = $grades->[0];
which means you could also have used the following:
my $grades = $students_grades{'Colton'}{'English'};
for my $grade (#$grades) {
print("$grade\n");
}
Knowing this allows one to easily escalate to the following:
for my $student_name (keys(%students_grades)) {
my $student_grades_by_class = $students_grades{$student_name};
for my $class_name (keys(%$student_grades_by_class)) {
my $grades = $student_grades_by_class->{$class_name};
for my $grade (#$grades) {
print("$student_name: $class_name: $grade\n");
}
}
}

Answer 2

In perl, for and foreach mean the same.
But the thing here is - you don't have a hash of arrays - you have a hash of array references.
So:
$students_grades{'Colton'}{'History'}
is actually an array reference.
So you can dereference it:
foreach my $grade ( #{ $students_grades{'Colton'}{'History'} } ) {
print "$grade\n";
}