Perl - Hashes

Hashes - Perl module P211

A hash is a collection of scalars, but each element can be named rather than numbered as it would be in a list. This makes it similar to a database table in many ways and leads to some truly remarkable capabilities.

This topic is presented on public courses Perl Programming, Perl bootcamp

Examples from our training material

acl	Sample answer - web_c2, page 152
bankout	initialising a hash
cbdemo	How sort callbacks work
env2	ENV module to import variables as globals
envrep	use of %ENV
h1	Setting up, adding to, changing a hash (associative array)
hash1.pl	setting up and using a hash
nip2	set up and loop though a hash in various ways
nip3	the danger of jumping out of an each loop
nip4	Sorting the keys of a hash
niports	hash - manipulation
peeps.pl	Set up a hash of people
so2	Sort using your own sort subroutine
so4	sort using a more complex routine
so5	sorting with a comparison block
sorter	Demonstration of default dort order
stdhash	keys must be unique - example illustrates the problem
stdhash3	Hash keys must be unique - so make up a new keu
stdhash4	Keys must be unique - design new keys, add accessor loops to find multiple keys
sthash2	Keys must be unique - solution 1 - Append all possible values
ukports	fill and look up a hash
web_count	Sample answer - web access counter question 1
webc2	Sample answer - 2nd question

Opentalk forum discussions related to this topic

Summation of file size according to user
sorting the spread sheet
Sorting a list of hashes
Sorting Data
Running another app with a changed environment
Removing duplicate lines with a regular expression
Reformatting question
Is this a hash in an SQL insert statement
Another large text file example
sorting program for golf scores

Pictures

Everyone's concentrating on the exercise

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from http://www.training-notes.co.uk.

Topics covered in this module

What is a hash?
Setting up a hash.
Keys and values.
Accessing a hash.
Processing every element.
Sorting.
cmp and operators.
Programming techniques for hashes.
Deleting hash elements.
Special hashes.
The environment.

Complete learning

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We have a technical library of over 600 books on the subjects on which we teach. These books are available for reference at our training centre. Also available is the Opentalk Forum for discussion of technical questions.