map, grep and $_ save loops
Topicalization and Special Variables example from a Well House Consultants training course
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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
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