[Za-pm] Hashes

[Nico Coetzee]

On Thursday 05 June 2003 12:24, Theunis De Klerk wrote:
> Hi Everyone,
>
> I'm a newbie, especially to Perl.So could someone please explain what
> hashes are and what they are used for. From what i see they are sort of
> like multi demensional arrays . Is that right?
>
> Muchly appreciated!!!
> Theunis
>
<snip>

Think of them as a big cupboard with many drawers. Each label on a drawer is 
an index, and if I open that drawer, I get the contents or value.

Let's say our cupboard holds personal info of various people, like their 
e-mail address. The trick is that the index of a hash, must be the pipece of 
information that uniquely identifies that data. In our example, names can be 
duplicated - I know I share my name with some judge, and one or two other 
"Nico Coetzee's" out there. What uniquely identifies me, is my e-mail 
address, for example, nico at whereever.com. I will then use the e-mail as the 
index:

$people{ "nico at whereever.com" } = "Nico Coetzee";

Because we now have an index, we can use that same index to store other bits 
of info in other cupboards, or hashes:

$cellnr{ "nico at whereever.com" } = "000 000 0000";

Each time, we just add another person's data, by using his/her e-mail as the 
index. In the end, I can then get a list of everybodies cell nr's like this:

foreach $key ( keys %people ) {
	$name = $people{ $key };
	$cell = $cellnr{ $key };
	print "$name => $cell\n";
}

We are now looping through the hash, using the keys of the hash as a 
reference. With each loop, we use the value of the $key variable to extract 
the information from the hashes - this is optional, and you could combine it 
all in one row, but for me personally it sometimes makes more sense to do it 
this way ( logically ).

Better look out for that articles :)

Hope this helps somewhat

Cheers

-- 
Nico Coetzee

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