In Perl, you can process whole lists (arrays) in single operations - and that's very efficient at run time as it avoids the needs for loops, and the needed for Perl's Virtual Machine to go back to the byte code (in effect source) for each member.

The map function applies an opertion to each member of a list, and returns a list of the same length, with each element duely mapped. The input to the transform function is $_ - so with embedded calls to functions like uc there's no need to specify it. But if you're going to take 1 off each member then you'll find $_ turn up in the code.

The grep function applies an operation to each member of a list, and returns the member unaltered for inclusion in the output list if the result is a true value. Otherwise, the input member is not included in the output list. So the output list from grep is going to be shorter than the incoming list, but the members themselves won't be modified.

@numbers = (10,30,40,33,45,32,43,22);
 
# Subtract 1 of each member of @numbers
@numbers = map($_-1,@numbers);
# Return a list of all numbers that are possible days of the month
@digit = grep( $_ <=31 ,@numbers);
 
print ("@digit\n");
 
@people = ("tim","steve","JASPER","DaVeY");
 
# Force all input members to lower case, then capitalise the first letter
@people = map(ucfirst lc,@people);
print "@people\n";
(written 2007-08-23 11:14:03)

 P208 - Perl - Lists
P669 - Perl - Data Munging

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Perl for Larger Projects - Object Oriented Perl
Customer feedback - lifeblood of a business
Well House Manor - feature comparison against the old place!
2008 course schedule - Perl, Python, PHP, Linux, Java Deployment, Ruby and more
Filtering and altering Perl lists with grep and map
Two years of campaigning for a train service
Business travel by train in the USA
Tratum Technologies
Some one line Perl tips and techniques
What do people look for on a hotel web site?