The PDL definition for bad value handling.
What you are reading is the pod documentation as extracted directly from the .pd file, which is not what you will see reported on your own machine. (I'm guessing you're reading this from CPAN.) What you see on your own machine depends on your PDL's configuration, as discussed near the bottom of this document.
The contents of Bad.pm depend on whether we have bad-value support in PDL.
If we do not have bad support then the module just contains a set of methods which essentially do nothing (they may return 0 or undef or a copy of the input piddle [thankfully PDL::copy handles inplace ops])
Up to, and including, v2.3.4 of PDL, this module added the badvalue and orig_badvalue routines to the PDL::Type package. They have now been moved to Basic/Core/Types.pm.PL where they belong.
If you don't have bad value support enabled, your docs for this module will look something like this.
PDL::Bad - PDL does not process bad values
PDL has been compiled with WITH_BADVAL either 0 or undef, so it does not contain any bad-value support code. Actually, a number of methods are defined, but they are only placeholders to make writing other code, that has to handle WITH_BADVAL being true or false, easier.
Implementation details are given in PDL::BadValues.
use PDL::Bad;
print "\nBad value support in PDL is turned " .
$PDL::Bad::Status ? "on" : "off" . ".\n";
Bad value support in PDL is turned off.
There are currently three variables that this module defines which may be of use.
Set to 0
Set to 0
Set to 0
PDL::Bad - PDL does process bad values
PDL has been compiled with WITH_BADVAL set to 1. Therefore, you can enter the wonderful world of bad value support in PDL.
This module is loaded when you do use PDL, Use PDL::Lite or PDL::LiteF.
Implementation details are given in PDL::BadValues.
use PDL::Bad;
print "\nBad value support in PDL is turned " .
$PDL::Bad::Status ? "on" : "off" . ".\n";
Bad value support in PDL is turned on.
and some other things
There are currently three variables that this module defines which may be of use.
Set to 1
Set to 1 if PDL was compiled with BADVAL_USENAN set, 0 otherwise.
Set to 1 if PDL was compiled with the experimental BADVAL_PER_PDL option set, 0 otherwise.
The experimental BADVAL_PER_PDL configuration option, which - when set - allows per-piddle bad values, was added after the 2.4.2 release of PDL. The $PDL::Bad::PerPdl variable can be inspected to see if this feature is available.
switch on/off/examine bad data flag
if ( $a->badflag() ) {
print "Data may contain bad values.\n";
}
$a->badflag(1); # set bad data flag
$a->badflag(0); # unset bad data flag
A return value of 1 does not guarantee the presence of bad data in a piddle; all it does is say that we need to check for the presence of such beasties. To actually find out if there are any bad values present in a piddle, use the check_badflag method.
Does support bad values.
returns the value used to indicate a missing (or bad) element for the given piddle type. You can give it a piddle, a PDL::Type object, or one of $PDL_B, $PDL_S, etc.
$badval = badvalue( float );
$a = ones(ushort,10);
print "The bad data value for ushort is: ",
$a->badvalue(), "\n";
If a new value is supplied via a piddle (e.g. $a->badvalue(23)), then the data in the supplied piddle is converted to use the new bad value as well if the data type is an integer or $PDL::Bad::UseNaN == 0.
Currently there is no way of automatically converting the bad values of already existing piddles. This could be supported - e.g. by having a per-piddle bad value or by storing a time index in the piddle structure - if required.
If the $PDL::Bad::PerPdl flag is set then it is possible to change the bad value on a per-piddle basis, so
$a = sequence (10);
$a->badvalue (3); $a->badflag (1);
$b = sequence (10);
$b->badvalue (4); $b->badflag (1);
will set $a to be [0 1 2 BAD 4 5 6 7 8 9] and $b to be [0 1 2 3 BAD 5 6 7 8 9]. If the flag is not set then both $a and $b will be set to [0 1 2 3 BAD 5 6 7 8 9]. Please note that the code to support per-piddle bad values is experimental in the current release.
Does support bad values.
returns the original value used to represent bad values for a given type.
This routine operates the same as badvalue, except you can not change the values.
It also has an awful name.
$orig_badval = orig_badvalue( float );
$a = ones(ushort,10);
print "The original bad data value for ushort is: ",
$a->orig_badvalue(), "\n";
Does support bad values.
clear the bad-value flag of a piddle if it does not contain any bad values
Given a piddle whose bad flag is set, check whether it actually contains any bad values and, if not, clear the flag. It returns the final state of the bad-value flag.
print "State of bad flag == ", $pdl->check_badflag;
Does support bad values.
Is a value bad?
Returns a 1 if the value is bad, 0 otherwise. Also see isfinite.
$a = pdl(1,2,3); $a->badflag(1); set($a,1,$a->badvalue); $b = isbad($a); print $b, "\n"; [0 1 0]
Is a value good?
Returns a 1 if the value is good, 0 otherwise. Also see isfinite.
$a = pdl(1,2,3); $a->badflag(1); set($a,1,$a->badvalue); $b = isgood($a); print $b, "\n"; [1 0 1]
Find the number of bad elements along the 1st dimension.
This function reduces the dimensionality of a piddle by one by finding the number of bad elements along the 1st dimension.
By using xchg etc. it is possible to use any dimension.
$a = nbadover($b);
$spectrum = nbadover $image->xchg(0,1)
Find the number of good elements along the 1st dimension.
This function reduces the dimensionality of a piddle by one by finding the number of good elements along the 1st dimension.
By using xchg etc. it is possible to use any dimension.
$a = ngoodover($b);
$spectrum = ngoodover $image->xchg(0,1)
Returns the number of bad values in a piddle
$x = nbad($data);
Does support bad values.
Returns the number of good values in a piddle
$x = ngood($data);
Does support bad values.
Set the value to bad at a given position.
setbadat $piddle, @position
@position is a coordinate list, of size equal to the number of dimensions in the piddle. This is a wrapper around set and is probably mainly useful in test scripts!
pdl> $x = sequence 3,4 pdl> $x->setbadat 2,1 pdl> p $x [ [ 0 1 2] [ 3 4 BAD] [ 6 7 8] [ 9 10 11] ]
Supports badvalues.
Set elements bad based on the supplied mask, otherwise copy across the data.
$a = sequence(5,5); $a = $a->setbadif( $a % 2 ); print "a badflag: ", $a->badflag, "\n"; a badflag: 1
Unfortunately, this routine can not be run inplace, since the current implementation can not handle the same piddle used as a and mask (eg $a->inplace->setbadif($a%2) fails).
Also see setvaltobad and setnantobad.
The output always has its bad flag set, even if it does not contain any bad values (use check_badflag to check whether there are any bad values in the output). Any bad values in the input piddles are copied across to the output piddle.
Set bad all those elements which equal the supplied value.
$a = sequence(10) % 3; $a->inplace->setvaltobad( 0 ); print "$a\n"; [BAD 1 2 BAD 1 2 BAD 1 2 BAD]
This is a simpler version of setbadif, but this function can be done inplace. See setnantobad if you want to convert NaN/Inf to the bad value.
The output always has its bad flag set, even if it does not contain any bad values (use check_badflag to check whether there are any bad values in the output). Any bad values in the input piddles are copied across to the output piddle.
The behavior of these functions depend on whether PDL::Bad::UseNaN is set to a true value. For PDL as currently distributed, this is typically not the case, so the documentation for that case is subdivided out here:
Sets NaN/Inf values in the input piddle bad (only relevant for floating-point piddles). Can be done inplace.
As $PDL::Bad::UseNan == 1, this is just a copy with a call to check_badflag() thrown in.
$b = $a->setnantobad; $a->inplace->setnantobad;
Supports bad values.
Sets Bad values to NaN (only relevant for floating-point piddles). Can be done inplace.
As $PDL::Bad::UseNan == 1, this is just a copy, with the bad flag being cleared.
$b = $a->setbadtonan; $a->inplace->setbadtonan;
Supports bad values.
On the other hand, if usenan is not true, then any number can be used to designate a bad value, and this must be handled with greater care. This is the usual case, and the documentation in that case is this:
Sets NaN/Inf values in the input piddle bad (only relevant for floating-point piddles). Can be done inplace.
$b = $a->setnantobad; $a->inplace->setnantobad;
Sets Bad values to NaN (only relevant for floating-point piddles). Can be done inplace and it clears the bad flag.
$b = $a->setbadtonan; $a->inplace->setbadtonan;
Replace any bad values by a (non-bad) value.
Can be done inplace. Also see badmask.
$a->inplace->setbadtoval(23); print "a badflag: ", $a->badflag, "\n"; a badflag: 0
The output always has its bad flag cleared. If the input piddle does not have its bad flag set, then values are copied with no replacement.
Copies values from one piddle to another, setting them bad if they are bad in the supplied mask.
Can be done inplace.
$a = byte( [0,1,3] ); $mask = byte( [0,0,0] ); set($mask,1,$mask->badvalue); $a->inplace->copybad( $mask ); p $a; [0 BAD 3]
It is equivalent to:
$c = $a + $mask * 0
The way the PDL handles the various bad value settings depends on your compile-time configuration settings, as held in perldl.conf.
$PDL::Config{WITH_BADVAL}Set this configuration option to a true value if you want bad value support. The default setting is for this to be true.
$PDL::Config{BADVAL_USENAN}Set this configuration option to a true value if you want floating-pont numbers to use NaN to represent the bad value. If set to false, you can use any number to represent a bad value, which is generally more flexible. In the default configuration, this is set to a false value.
$PDL::Config{BADVAL_PER_PDL}Set this configuration option to a true value if you want each of your piddles to keep track of their own bad values. This means that for one piddle you can set the bad value to zero, while in another piddle you can set the bad value to NaN (or any other useful number). This is usually set to false.
Doug Burke (djburke@cpan.org), 2000, 2001, 2003, 2006.
The per-piddle bad value support is by Heiko Klein (2006).
CPAN documentation fixes by David Mertens (2010).
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.
