Setting up, then displaying contents, of a hash

Hashes example from a Well House Consultants training course
More on Hashes [link]

This example is described in the following article(s):
• Reactive (dynamic) formatting in Perl - [link]

Source code: ha1 Module: P211

=head1 Sample data

antonia Perl XML PHP Tcl/Tk MySQL
barbara Tcl/Tk Lua Ruby Java
[and so on]

With data like this, you'll want to be able to ask
questions like "does Barbara know Perl" and "what
skills does Xena have", rather than "what does the
10th person in my file know?". In other words,
you'll want to look things up by a key rather than
by a value.

In Perl, you should use a HASH for this purpose -
a hash is a collection of scalars, each keyed by
another scalar. Hashes differ from lists - the
other colelction type in Perl - as follows:
a) hashes are keyed by any scalar, not by number
b) hashes are unordered (i.e. not sorted/sortable)
c) hashes are referred to with a % not an @
d) hash members are accessed with {} and not []

=cut

open (FH,"../requests.xyz") or die();

while ($line = <FH>) {
        chop($line);
        ($name,$skills) = split(/\s+/,$line,2);
        # The hash is called %stab - but no need to
        # declare it as it's automatically created
        $stab{$name} = $skills;
        }

# You can't sort a hash but you CAN sort a list
# of the keys ....
@nems = reverse(sort byvalue (keys %stab));
# ... and the step through each keyed item in turn

foreach $name (@nems) {
        print "$name --- $stab{$name}\n";
}

print "There are ",@nems+0," people\n";

# Sort routine - inputs are always $a and $b
# and output is -ve / 0 / +ve to indicate which
# way the two values in $a and $b should be ordered
sub byvalue {
        # Following print useful for training!
        # print "$a .......... $b\n";
        $stab{$a} cmp $stab{$b};
        }

__END__

Sample Output

Dorothy:p82 grahamellis$ perl ha1
petra --- XML Tcl/Tk Lua Perl Ruby
gloria --- XML Perl Tcl/Tk MySQL
margaret --- XML Perl Ruby MySQL Tcl/Tk
jenny --- XML Perl Ruby Lua
yuri --- XML PHP Perl Tcl/Tk
delia --- XML PHP Java Lua
tina --- Tcl/Tk Ruby Java
ken --- Tcl/Tk Python Java Perl
sally --- Tcl/Tk Perl XML MySQL
steve --- Tcl/Tk Perl PHP Ruby
quentin --- Tcl/Tk Perl PHP Ruby
nina --- Tcl/Tk Perl Lua Ruby
barbara --- Tcl/Tk Lua Ruby Java
victor --- Ruby Perl Tcl/Tk MySQL
william --- Ruby Perl PHP
ed --- Ruby Perl Java PHP
yollanda --- Ruby MySQL Tcl/Tk
zoe --- Ruby Lua Perl PHP
florence --- Ruby Lua PHP Java
ivan --- Ruby Java Perl Tcl/Tk MySQL
barry --- Python XML Java Perl PHP
adam --- Python Tcl/Tk Perl MySQL
antonia --- Perl XML PHP Tcl/Tk MySQL
kerry --- Perl Tcl/Tk Ruby MySQL
wendy --- Perl Tcl/Tk Lua MySQL
david --- Perl Tcl/Tk Java
charles --- Perl Ruby MySQL Tcl/Tk
iris --- Perl MySQL Java Tcl/Tk
tommy --- Perl Java XML
cherry --- Perl Java Ruby MySQL
morris --- Perl Java PHP Tcl/Tk
len --- Perl Java MySQL Ruby
john --- PHP XML Java Perl
hazel --- PHP Python Perl Ruby Lua
leane --- PHP Python Lua Perl Java
nigel --- PHP Python Java Perl
harry --- PHP Python Java
rita --- PHP Lua Ruby Perl
peter --- PHP Java Perl
xavier --- PHP Java Perl
orpheus --- MySQL Ruby Tcl/Tk XML
olivia --- MySQL Python Lua PHP
ethel --- MySQL Perl Tcl/Tk Lua
fred --- MySQL Perl Java XML
uva --- MySQL Perl Java PHP
zachary --- MySQL Java Tcl/Tk
queenie --- Lua Ruby Perl MySQL
graham --- Lua Perl Tcl/Tk
rupert --- Java Python MySQL
venus --- Java Perl Ruby Lua
xena --- Java Perl PHP Lua XML
ulsyees --- Java PHP Perl
There are 52 people
Dorothy:p82 grahamellis$

Learn about this subject

This module and example are covered on the following public courses:
* Perl Programming
* Perl bootcamp
* Learning to program in Perl
* Perl Programming
Also available on on site courses for larger groups

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