Bad(3) User Contributed Perl Documentation Bad(3)NAMEPDL::Bad - PDL does process bad values
DESCRIPTION
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.
SYNOPSIS
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
VARIABLES
There are currently three variables that this module defines which may
be of use.
$PDL::Bad::Status
Set to 1
$PDL::Bad::UseNaN
Set to 1 if PDL was compiled with "BADVAL_USENAN" set, 0 otherwise.
$PDL::Bad::PerPdl
Set to 1 if PDL was compiled with the experimental "BADVAL_PER_PDL"
option set, 0 otherwise.
FUNCTIONS
badflag
getter/setter for the 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
When called as a setter, this modifies the piddle on which it is
called. This always returns a Perl scalar with the final value of the
bad 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.
This function works with piddles that have bad values. It always
returns a Perl scalar, so it never returns bad values.
badvalue
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: ",
$a->badvalue(), "\n";
This can act as a setter (e.g. "$a->badvalue(23)") if the data type is
an integer or "$PDL::Bad::UseNaN == 0". Note that this never touches
the data in the piddle. That is, if $a already has bad values, they
will not be changed to use the given number and if any elements of $a
have that value, they will unceremoniously be marked as bad data. See
"setvaltobad", "setbadtoval", and "setbadif" for ways to actually
modify the data in piddles
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, and it
requires that you modify the settings under which PDL is compiled.
This method does not care if you call it on an input piddle that has
bad values. It always returns a Perl scalar with the current or new bad
value.
orig_badvalue
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";
This method does not care if you call it on an input piddle that has
bad values. It always returns a Perl scalar with the original bad value
for the associated type.
check_badflag
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;
This method accepts piddles with or without bad values. It returns a
Perl scalar with the final bad-value flag, so it never returns bad
values itself.
isbad
Signature: (a(); int [o]b())
Returns a binary mask indicating which values of the input are bad
values
Returns a 1 if the value is bad, 0 otherwise. Similar to isfinite.
$a = pdl(1,2,3);
$a->badflag(1);
set($a,1,$a->badvalue);
$b = isbad($a);
print $b, "\n";
[0 1 0]
This method works with input piddles that are bad. The ouptut piddle
will never contain bad values, but its bad value flag will be the same
as the input piddle's flag.
isgood
Signature: (a(); int [o]b())
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]
This method works with input piddles that are bad. The ouptut piddle
will never contain bad values, but its bad value flag will be the same
as the input piddle's flag.
nbadover
Signature: (a(n); int+ [o] b())
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. In this sense it
shares much in common with the functions defined in PDL::Ufunc. In
particular, by using xchg and similar dimension rearranging methods, it
is possible to perform this calculation over any dimension.
$a = nbadover($b);
$spectrum = nbadover $image->xchg(0,1)
nbadover processes input values that are bad. The ouput piddle will not
have any bad values, but the bad flag will be set if the input piddle
had its bad flag set.
ngoodover
Signature: (a(n); int+ [o] b())
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)
ngoodover processes input values that are bad. The ouput piddle will
not have any bad values, but the bad flag will be set if the input
piddle had its bad flag set.
nbad
Returns the number of bad values in a piddle
$x = nbad($data);
Accepts good and bad input piddles; output is a Perl scalar and
therefore is always good.
ngood
Returns the number of good values in a piddle
$x = ngood($data);
Accepts good and bad input piddles; output is a Perl scalar and
therefore is always good.
setbadat
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]
]
This method can be called on piddles that have bad values. The
remainder of the arguments should be Perl scalars indicating the
position to set as bad. The ouptut piddle will have bad values and will
have its badflag turned on.
setbadif
Signature: (a(); int mask(); [o]b())
Set elements bad based on the supplied mask, otherwise copy across the
data.
pdl> $a = sequence(5,5)
pdl> $a = $a->setbadif( $a % 2 )
pdl> p "a badflag: ", $a->badflag, "\n"
a badflag: 1
pdl> p "a is\n$a"
[
[ 0 BAD 2 BAD 4]
[BAD 6 BAD 8 BAD]
[ 10 BAD 12 BAD 14]
[BAD 16 BAD 18 BAD]
[ 20 BAD 22 BAD 24]
]
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). Even more unfortunate: we
can't catch this error and tell you.
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). The input piddle can have bad values: any bad values
in the input piddles are copied across to the output piddle.
Also see setvaltobad and setnantobad.
setvaltobad
Signature: (a(); [o]b(); double value)
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.
setnantobad
Signature: (a(); [o]b())
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;
This method can process piddles with bad values: those bad values are
propogated into the output piddle. Any value that is not finite is also
set to bad in the output piddle. If all values from the input piddle
are good and finite, the output piddle will not have its bad flag set.
One more caveat: if done inplace, and if the input piddle's bad flag is
set, it will no
setbadtonan
Signature: (a(); [o] b();)
Sets Bad values to NaN
This is only relevant for floating-point piddles. The input piddle can
be of any type, but if done inplace, the input must be floating point.
$b = $a->setbadtonan;
$a->inplace->setbadtonan;
This method processes input piddles with bad values. The output piddles
will not contain bad values (insofar as NaN is not Bad as far as PDL is
concerned) and the output piddle does not have its bad flag set. As an
inplace operation, it clears the bad flag.
setbadtoval
Signature: (a(); [o]b(); double newval)
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.
copybad
Signature: (a(); mask(); [o]b())
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
This handles input piddles that are bad. If either $a or $mask have bad
values, those values will be marked as bad in the output piddle and the
output piddle will have its bad value flag set to true.
CHANGES
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.
CONFIGURATION
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.
AUTHOR
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, 2013).
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 2014-01-17 Bad(3)
