Please please please could one of you turn the example into a *.t file which we
can use to permanently constrain PDL behaviour going forward?
Ed
From: Marek Gierliński
Sent: Tuesday, June 16, 2015 5:12 PM
To: Chris Marshall ; pdl-devel@lists.sourceforge.net
Subject: Re: [Pdl-devel] Fwd: Re: [Pdl-general] Weird behaviour of stats with
bad values
Thanks a lot, Chris!
Marek
On Tue, 16 Jun 2015 at 15:57 Chris Marshall <devel.chm...@gmail.com> wrote:
Marek-
I've opened a highest priority bug report based on your information:
http://sourceforge.net/p/pdl/bugs/390
Could you add information on your system specifics to the ticket
for reference (the output of perldl -V has the main information)?
We'll be updating the ticket as information becomes available.
Thanks for reporting the problem!
Chris
On 6/16/2015 09:49, Marek Gierliński wrote:
This is very bad news for me. I just searched through my scripts and found
586 instances of 'stats'. If this is not corrected, I have to assume that all
of them might potentially produce incorrect results, without even failing (like
in the if($s > 0) example).
We've been using 2.007 for a couple of months now. I'm not even sure if my
recent results are correct.
Marek
On Tue, 16 Jun 2015 at 14:43 Chris Marshall <devel.chm...@gmail.com> wrote:
That definitely seems like a bug to me. Thanks for the cross-check,
Marek.
Devels, I see the same in the latest PDL release so it is not a PDL-2.007
only issue.
--Chris
On 6/16/2015 09:36, Marek Gierliński wrote:
OK, thank you for your explanations. I'm not sure if all of this makes
sense. If you try
print $s > 5;
in the above example, you will get 'BAD'. 5 is just a scalar and not a
bad value. And $s is a one-dimensional piddle with a value different from the
bad value. Neither of the values in this conditional expression is bad. Why
does it return a string 'BAD'?
Marek
On Tue, 16 Jun 2015 at 14:24 Chris Marshall <devel.chm...@gmail.com>
wrote:
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 mailto:devel.chm...@gmail.com
To: Derek Lamb mailto:de...@boulder.swri.edu, Marek Gierliński
mailto: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> 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> 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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