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 CWuse PDL, CWUse PDL::Lite or CWPDL::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 two 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 CWBADVAL_USENAN set, 0 otherwise.

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 CW$PDL_B, CW$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. CW$a->badvalue(2)), then the data in the supplied piddle is converted to use the new bad value as well if the data type is an integer or CW$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.

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.

  Signature: (a(); int [o]b())

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]

isbad does handle bad values. The output piddles will NOT have their bad-value flag set.

  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]

isgood does handle bad values. The output piddles will NOT have their bad-value flag set.

  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.

By using xchg etc. it is possible to use any dimension.

 $a = nbadover($b);

 $spectrum = nbadover $image->xchg(0,1)

nbadover does handle bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

  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 does handle bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

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

CW@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!

 perldl> $x = sequence 3,4
 perldl> $x->setbadat 2,1
 perldl> p $x
 [
  [  0   1   2]
  [  3   4 BAD]
  [  6   7   8]
  [  9  10  11]
 ]

Supports badvalues.

  Signature: (a(); int mask(); [o]b())

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 CWa and CWmask (eg CW$a->inplace->setbadif($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.

  Signature: (a(); [o]b(); double value)

Set bad all those elements which equal the supplied value.

 $a = sequence(1) % 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.

Sets NaN/Inf values in the input piddle bad (only relevant for floating-point piddles). Can be done inplace.

As CW$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 CW$PDL::Bad::UseNan == 1, this is just a copy, with the bad flag being cleared.

 $b = $a->setbadtonan;
 $a->inplace->setbadtonan;

Supports bad values.

  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(2); 
 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.

  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

Handles bad values.

Doug Burke (djburke@cpan.org), 2000, 2001, 2003.

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