Reduce(3) User Contributed Perl Documentation Reduce(3)NAMEPDL::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 functions
(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
argument, 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
hopefully feel more at home.
$result = $pdl->reduce($operation [,@dims]);
"reduce" applies the named operation along the specified dimension(s)
reducing the input piddle dimension by as many dimensions as supplied
as arguments. If the dimension(s) argument is omitted the operation is
applied along the first dimension. To get a list of valid operations
see canreduce.
NOTE - new power user feature: you can now supply a code reference as
operation to reduce with.
# reduce by summing over dims 0 and 2
$result = $pdl->reduce(\&sumover, 0, 2);
It is your responsibility to ensure that this is indeed a PDL
projection operation that turns vectors into scalars! You have been
warned.
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 separated
from the PDL distribution, the copyright notice should be included in
the file.
perl v5.18.1 2013-05-12 Reduce(3)