map, grep and $_ save loops
Topicalization and Special Variables example from a Well House Consultants training course
More on Topicalization and Special Variables [link]
Source code: exact Module: P210
=head1 Map and Grep save loops
Perl's map and grep functions allow
you to process every member of a list.
With grep, you're performing a test on
each list member and producting a new
list which contains only those members
for which the test is true. Although
the usual use of grep is with a regular
expression, in fact it can handle any
logical test ... each of the items of
the incoming list is placed, in turn,
in $_ and the test performed.
Map also places each element in turn in
$_, but rather than returning a shorted
list of elements which are identical to
elements in the original list, it returns
a list of all elements, but transformed
through the mapping given.
In this example, we use "grep" to see
which companies on our industrial estate
have an exact multiple of 11 members of
staff (perhaps we're making up cricket
teams), and we use "map" to get a count
of the number of teams for every company.
@staff = (4000, 2500, 44, 121, 144, 161);
@teams = grep (($_ % 11 == 0), @staff);
print "exacts ... @teams\n";
@ntms = map(int($_/11),@staff);
print "number of teams ... @ntms\n";
Dorothy:ppcsrd08 grahamellis$ perl exact
exacts ... 44 121
number of teams ... 363 227 4 11 13 14
Learn about this subject
This module and example are covered on the following public courses:
* Perl Programming
* Perl bootcamp
Also available on on site courses for larger groups
Books covering this topic
Yes. We have over 700 books in our library. Books covering Perl are listed here and when you've selected a relevant book we'll link you on to Amazon to order.
This example comes from our "Topicalization and Special Variables" training module. You'll find a description of the topic and some other closely related examples on the "Topicalization and Special Variables" module index page.
Full description of the source code
The complete training module that describes this source code is availble for download (for limited use) from our download centre.
• Our Solutions centre provides a number of longer technical articles.
• Our Opentalk forum archive provides a question and answer centre.
• The Horse's mouth provides a daily tip or thought.
• Further resources are available via the resources centre.
• All of these resources can be searched through through our search engine
• And there's a global index here.
Web site author
This web site is written and maintained by Well House Consultants.
Purpose of this website
This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.
Conditions of use
Past attendees on our training courses are welcome to use individual examples in the course of their programming, but must check the examples they use to ensure that they are suitable for their job. Remember that some of our examples show you how not to do things - check in your notes. Well House Consultants take no responsibility for the suitability of these example programs to customer's needs.
This program is copyright Well House Consultants Ltd. You are forbidden from using it for running your own training courses without our prior written permission. See our page on courseware provision for more details.
Any of our images within this code may NOT be reused on a public URL without our prior permission. For Bona Fide personal use, we will often grant you permission provided that you provide a link back. Commercial use on a website will incur a license fee for each image used - details on request.
PH: 01144 1225 708225 • FAX: 01144 1225 899360 • EMAIL: email@example.com • WEB: http://www.wellho.net • SKYPE: wellho
PAGE: http://www.wellho.net/resources/ex.php4 • PAGE BUILT: Sat Apr 13 08:12:34 2013 • BUILD SYSTEM: wizard