Reduce(3)						User Contributed Perl Documentation						 Reduce(3)

NAME

       PDL::Reduce -- a "reduce" function for PDL

DESCRIPTION

       Many languages have a "reduce" function used to reduce the rank of an N-D array by one. It works by applying a selected operation along a
       specified dimension. This module implements such a function for PDL by providing a simplified interface to the existing projection func-
       tions (e.g. "sumover", "maximum", "average", etc).

SYNOPSIS

	use PDL::Reduce;
	$a = sequence 5,5;
	# reduce by adding all
	# elements along 2nd dimension
	$b = $a->reduce('add',1);
	@ops = $a->canreduce; # return a list of all allowed operations

FUNCTIONS

       reduce

       reduce dimension of piddle by one by applying an operation along the specified dimension

	$a = sequence 5,5;
	# reduce by adding all
	# elements along 2nd dimension
	$b = $a->reduce('add',1);
	$b = $a->reduce('plus',1);
	$b = $a->reduce('+',1);     # three ways to do the same thing

       [ As an aside: if you are familiar with threading you will see that this is actually the same as

	$b = $a->mv(1,0)->sumover

       ]

       NOTE: You should quote the name of the operation (1st arg) that you want "reduce" to perform. This is important since some of the names are
       identical to the names of the actual PDL functions which might be imported into your namespace. And you definitely want a string as argu-
       ment, not a function invocation! For example, this will probably fail:

	 $b = $a->reduce(avg,1); # gives an error from invocation of 'avg'

       Rather use

	 $b = $a->reduce('avg',1);

       "reduce" provides a simple and unified interface to the projection functions and makes people coming from other data/array languages hope-
       fully feel more at home.

	$result = $pdl->reduce($operation [,$dim]);

       "reduce" applies the named operation along the specified dimension reducing the input piddle dimension by one. If the dimension is omitted
       the operation is applied along the first dimension. To get a list of valid operations see canreduce.

       canreduce

       return list of valid named "reduce" operations Some common operations can be accessed using a number of names, e.g. '+', "add" and "plus"
       all sum the elements along the chosen dimension.

	 @ops = PDL->canreduce;

       This list is useful if you want to make sure which operations can be used with "reduce".

AUTHOR

       Copyright (C) 2000 Christian Soeller (c.soeller@auckland.ac.nz). All rights reserved. There is no warranty. You are allowed to redistribute
       this software / documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is sepa-
       rated from the PDL distribution, the copyright notice should be included in the file.

perl v5.8.0							    2001-07-07								 Reduce(3)