Hi there,
Me again. The sort function does NOT default to <=>. It defaults to string
comparison order. See the Perl doc for sort:
"If SUBNAME or BLOCK is omitted, sorts in standard string comparison
order. "
So assuming you want numbers sorting, 'sort { $a <=> $b } keys %{$nameref}'
would be the way to go.
On Sat, Sep 10, 2016, 4:11 PM Jim Gibson <[email protected]> wrote:
>
> > On Sep 9, 2016, at 8:54 AM, Nathalie Conte <[email protected]> wrote:
> >
> > Hello,
> > I have a question about making a calculation within a loop
> >
> > I have a hash of hashes
> > ##############
> > #!/usr/bin/perl
> > use strict;
> > use warnings;
> >
> > use Data::Dumper qw(Dumper);
> >
> > my %grades;
> > $grades{"Foo "}{1} = 97;
> > $grades{"Foo "}{2} = 107;
> > $grades{"Peti "}{1} = 88;
> > $grades{"Peti "}{3} = 89;
> > $grades{"Peti "}{4} = 99;
> >
> > print Dumper \%grades;
> > print "----------------\n";
> >
> > foreach my $name ( keys %grades) {
> > foreach my $subject (sort {$a <=> $b} keys %{ $grades{$name} }) {
> > print "$name, $subject: $grades{$name}{$subject}\n";
> > }
> > }
> >
> > ##############
> > output is
> > $VAR1 = {
> > 'Peti ' => {
> > '4' => 99,
> > '1' => 88,
> > '3' => 89
> > },
> > 'Foo ' => {
> > '1' => 97,
> > '2' => 107
> > }
> > };
> > ----------------
> > Peti , 1: 88
> > Peti , 3: 89
> > Peti , 4: 99
> > Foo , 1: 97
> > Foo , 2: 107
> > ###############
> > Now, what I would like to achieve:
> > I want to make a calculation, in each $name (Peti and Foo), calculate:
> > for Peti:
> > first line : no action
> > second line -(minus) 1st line:
> > print subject 3-1=2, 89-88=1
> > third line - 2nd line:
> > print subject 4-3=1, 99-89=10
> >
> > for foo:
> > first line : no action
> > second line -(minus) 1st line:
> > print subject 2-1=2, 107-97=10
> >
>
> For each $name, declare two variables ($prev_subject and $prev_grade
> below) to hold the subject and grade. These variables will be undefined
> during the first pass through the inner loop:
>
> for my $name ( keys %grades ) {
> my $nameref = $grades{$name}; # do one hash lookup
> my( $prev_subject, $prev_grade );
> for my $subject ( sort keys %{$nameref} ) { # {$a<=>$b} is the default
> for sort
> my $grade = $nameref->{$subject};
> if( defined $prev_subject ) {
> my $subject_delta = $subject = $prev_subject;
> my $grade_delta = $grade - $prev_grade;
> print "$name: $subject_delta: $grade_delta\n";
> }
> $prev_subject = $subject;
> $prev_grade = $grade;
> }
> }
>
>
>
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>
>
>
