How can one access all the details of a person using arrays & hash?

[supriyoch_2008]

Hi PerlMonks,

I am interested to access the data for a student using the query of Registration number. I have no idea about making a database. So I have thought of using the arrays to get the detailed information. Is it possible to get the desired results using arrays and hash as given in the following script (incomplete)? I request Perlmonks to provide some suggestions in this matter.

#!/usr/bin/perl  
use warnings;
use strict;   
#################################
## HASH OF ARRAYS: 
#################################
my @a=qw/A B C D/; 
my @b=qw/20 19 22 23/; 
my @c=qw/x1 x2 x3 x4/;
my @d=qw/phone4 phone2 phone3 phone1/;
my @e=qw/72 55 83 69/; 
my @f=qw/2011 2012 2009 2008/;
 
# HASH of arrays: 
my %hash=('Name' => @a, 'Age' => @b, 'Regd_no' => @c,
       'Phone_num'=> @d, 'Marks' => @e, 'Pass_year'=> @f); 

## To access all the information with the query of Regd Number: 
print"\n Enter the regd number (say x3): "; 
 my $entry=<STDIN>; 
## Code for accessing individual student information ??? (Not known)

## Code for inserting & deleting the details of a student ???

exit;

Result should look like:

Regd No. x3 has the following details:

Name: C

Age : 22

Phone_num: phone3

Marks: 83

Pass_Year: 2009

[Athanasius]

Distributing the data for a single student across multiple arrays is asking for trouble. Much better to keep each student’s data in the same structure. So I would reverse the architecture: instead of a hash of arrays, use an array of hashes. Or, more precisely, an array of blessed hashes (objects). Something like this:

#! perl
use strict;
use warnings;

{
    package Student;

    sub new
    {
        my ($class,   $name,      $age,
            $regd_no, $phone_num, $mark, $pass_year) = @_;
        my  $self = {
                        NAME    => $name,    AGE       => $age,
                        REGD_NO => $regd_no, PHONE_NUM => $phone_num,
                        MARK    => $mark,    PASS_YEAR => $pass_year
                    };

        return bless $self, $class;
    }

    sub display
    {
        my ($self) = @_;

        if ($self)
        {
            print 'Name:       ', $self->{NAME},      "\n";
            print 'Age:        ', $self->{AGE},       "\n";
            print 'Regd no:    ', $self->{REGD_NO},   "\n";
            print 'Phone num:  ', $self->{PHONE_NUM}, "\n";
            print 'Mark:       ', $self->{MARK},      "\n";
            print 'Pass year:  ', $self->{PASS_YEAR}, "\n";
        }
    }
}

my @students;

while (<DATA>)
{
    chomp;
    push @students, Student->new(split /:/);
}

find_student('x3')->display();

sub find_student
{
    my ($regd_no) = @_;

    for (@students)
    {
        return $_ if $_->{REGD_NO} eq $regd_no;
    }

    return undef;
}

__DATA__
A:20:x1:phone4:72:2011
B:19:x2:phone2:55:2012
C:22:x3:phone3:83:2009
D:23:x4:phone1:69:2008

Output:

17:18 >perl 578_SoPW.pl
Name:       C
Age:        22
Regd no:    x3
Phone num:  phone3
Mark:       83
Pass year:  2009

17:22 >

Hope that helps,

[supriyoch_2008]

Hi Athanasius,

Thanks for your prompt reply. I shall try to understand the code given by you. Should I find any difficulty, I shall let you know.

With deep regards,

[CountZero]

I have no idea about making a database.

Like it or not, even your array of hashrefs or hash of arrayrefs are the building blocks of a database. But rather than stumble in the dark and (badly) re-invent databases, spend some time studying database design and theory. It is knowledge that will pay itself back over and over again. This Wikiversity link is not a bad place to start.

[topher]

For a case like this, I probably wouldn't use arrays. I'd use a Hash of Hashes for the students. The outer hash would key on the registration number, with its value being a second hash that contains the student details. That'll give you a more self-documenting data structure that allows direct access to any student by registration number.

If I was going to use arrays somewhere, I would recommend strongly against using them the way you are. Not to be mean, but the data structure as you have it written is probably the worst way to do it. You don't want to split up related data across multiple data structures (in your case, multiple arrays). You'd be better off using an array of arrays (or hashes), assuming you were always going to "process" all student entries every time. Or, use a hash of arrays, using the array to hold the details for each individual student, and hashing on the registration number.

Here's an example of using the Hash of Hashes I described above:

#!/usr/bin/env perl
use strict;
use warnings;

my %students;
my $key = shift || 0;

while (<DATA>) {
    chomp;
    my ( $name, $age, $reg_no, $phone, $marks, $year ) = split ":";

    $students{$reg_no} = { name  => $name,
                           age   => $age,
                           phone => $phone,
                           marks => $marks,
                           year  => $year,
                         };
}

if ($key) {
    # Print the details of our preselected student
    print "Information for student with registration number $key is: \
+n";
    print " Name: " . $students{$key}{name} . "\n";
    print " Age: " . $students{$key}{age} . "\n";
    print " Phone: " . $students{$key}{phone} . "\n";
    print " Marks: " . $students{$key}{marks} . "\n";
    print " Year: " . $students{$key}{year} . "\n";
}
else {
    # Print the name for each student we have a record for
    print "List of all students:\n";
    foreach my $id ( sort keys %students ) {
        print " Registration Number: " . $id . "\n";
        print "   Name: " . $students{$id}{name} . "\n";
    }
}

__DATA__
John Doe:20:x1:555-1234:50:2013
Jane Doe:19:x2:555-4321:55:2012
Bob Smith:22:x3:555-2468:90:2011
Mortimer Jones:18:x4:555-0313:77:2008

And some sample outputs of running the above code:

topher@nexus:~/foo$ ./student-HoH.pl
List of all students:
 Registration Number: x1
   Name: John Doe
 Registration Number: x2
   Name: Jane Doe
 Registration Number: x3
   Name: Bob Smith
 Registration Number: x4
   Name: Mortimer Jones
topher@nexus:~/foo$ ./student-HoH.pl x4
Information for student with registration number x4 is:
 Name: Mortimer Jones
 Age: 18
 Phone: [phone]
 Marks: 77
 Year: 2008