This result seems to violate the principle of least surprise.
On the LHS we have a PDL with badvalue(0) and on the RHS we
have a perl scalar with value 0 (which happens to be the bad
value for the PDL).
It seems surprising that $pdl > 0 is actually $pdl > pdl(0)->badvalue(0)
Thoughts?
Chris
-------- Forwarded Message --------
Subject: Re: [Pdl-general] Weird behaviour of stats with bad values
Date: Tue, 16 Jun 2015 09:18:29 -0400
From: Chris Marshall <devel.chm...@gmail.com>
To: Derek Lamb <de...@boulder.swri.edu>, Marek Gierliński
<marek.gierlin...@gmail.com>
CC: pdl-gene...@lists.sourceforge.net
I think the problem is that if $s is a badvalue piddle with the badvalue=0
then $s>0 is $s>BAD which is BAD. If you use a value for badvalue that is
not in the comparison, you should be good.
--Chris
On 6/16/2015 09:11, Derek Lamb wrote:
Thanks for the simple example. That helps a lot.
The actual problem is that piddles with the badflags set always
evaluate to BAD when element-wise logical operations are performed on
them.
"print $s<0" prints BAD instead of 0 or 1. "print $x>0" also prints
[BAD BAD BAD BAD].
$m and $s have their badflags set (as they should, since they were
made from partially-bad data). You can check if they can be safely
cleared, and clear them if so, with $s->check_badflag, etc. Since $m
and $s are 1-element piddles, you can also just set them directly to
their scalar values, for example
map{$_=$_->sclr} ($m,$s)=stats($x); #if you know they are only going
to be 1 element piddles
OR
map{$_=$_->((0))} ($m,$s)=stats($x); #if you just want the first value
The fact that $m and $s are 1-element piddles is likely what is
causing your problem. My guess is that this behavior has changed
(perhaps intentionally, perhaps not) between your old version and more
recent versions, and if you were getting $m and $s as simple perl
scalars before you would not have seen this problem. I can verify
that stats() has returned 1-piddles and not perl scalars at least as
far back as PDL-2.4.11.
cheers,
Derek
On Jun 16, 2015, at 6:29 AM, Marek Gierliński
<marek.gierlin...@gmail.com <mailto:marek.gierlin...@gmail.com>> wrote:
Oops, sorry, I missed a line when copying the text. Here is the code
again.
use PDL;
use PDL::NiceSlice;
my $x = pdl(1, 2, 3, 0);
$x->badflag(1);
$x->badvalue(0);
print "x = $x\n";
my ($m, $s) = stats($x);
print "m = $m, s = $s\n";
print "s greater than zero\n" if $s > 0;
print "s less than zero\n" if $s < 0;
print "s equals zero\n" if $s == 0;
On Tue, 16 Jun 2015 at 12:20 Chris Marshall <devel.chm...@gmail.com
<mailto:devel.chm...@gmail.com>> wrote:
Hi Marek-
Do you have a complete example showing the problem?
You don't show where $m and $s are being set below.
Thanks,
Chris
On 6/16/2015 07:04, Marek Gierliński wrote:
I have recently encountered a weird problem with stats (or
statsover) using bad values. The resulting numbers have a
strange property, they always return true in comparisons. This
code:
use PDL;
use PDL::NiceSlice;
my $x = pdl(1, 2, 3, 0);
$x->badflag(1); $x->badvalue(0);
print "m = $m, s = $s\n";
print "s greater than zero\n" if $s > 0;
print "s less than zero\n" if $s < 0;
print "s equals zero\n" if $s == 0;
returns the following output:
x = [1 2 3 BAD]
m = 2, s = 1
s greater than zero
s less than zero
s equals zero
which doesn't make any sense. Can anyone explain this? I always
assumed that 'stats' returned ordinary Perl scalars, but this
must be something different.
I'm using PDL version 2.007. We had an older version installed
for a long time and I think this problem appeared when we
upgraded to 2.007.
Marek
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