Thread: [matplotlib-devel] Bug: plot numpy.nans vs. datetime objects

Hi all,

I get a ValueError, if I try to plot a list of numpy.nans against
datetime objects. I'm using Python 2.6.5 and Matplotlib 1.0.1 on Ubuntu
Linux 10.04. Code and traceback are below.

Best regards,
Gerrit



Code
""""
import matplotlib.pyplot as plt
import numpy as np
from datetime import datetime as DateTime

t = [DateTime(2011,1,day) for day in xrange(1,20)]
x = [np.nan for i in xrange(1,20)]

plt.plot(t,x)
plt.show()


Traceback
"""""""""
Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python2.6/lib-tk/Tkinter.py", line 1413, in __call__
    return self.func(*args)
  File
"/usr/local/lib/python2.6/dist-packages/matplotlib/backends/backend_tkagg.py", line 245, in resize
    self.show()
  File
"/usr/local/lib/python2.6/dist-packages/matplotlib/backends/backend_tkagg.py", line 248, in draw
    FigureCanvasAgg.draw(self)
  File
"/usr/local/lib/python2.6/dist-packages/matplotlib/backends/backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/artist.py",
line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/figure.py",
line 798, in draw
    func(*args)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/artist.py",
line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/axes.py", line
1946, in draw
    a.draw(renderer)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/artist.py",
line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/axis.py", line
971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/axis.py", line
904, in iter_ticks
    majorLocs = self.major.locator()
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/dates.py",
line 743, in __call__
    self.refresh()
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/dates.py",
line 752, in refresh
    dmin, dmax = self.viewlim_to_dt()
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/dates.py",
line 524, in viewlim_to_dt
    return num2date(vmin, self.tz), num2date(vmax, self.tz)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/dates.py",
line 289, in num2date
    if not cbook.iterable(x): return _from_ordinalf(x, tz)
  File "/usr/local/lib/python2.6/dist-packages/matplotlib/dates.py",
line 203, in _from_ordinalf
    dt = datetime.datetime.fromordinal(ix)
ValueError: ordinal must be >= 1

Gerrit Kuhlmann, on 2011-03-25 14:26,  wrote:
> Hi all,
> 
> I get a ValueError, if I try to plot a list of numpy.nans against
> datetime objects. I'm using Python 2.6.5 and Matplotlib 1.0.1 on Ubuntu
> Linux 10.04. Code and traceback are below.
> 
> Best regards,
> Gerrit
> 
> 
> 
> Code
> """"
> import matplotlib.pyplot as plt
> import numpy as np
> from datetime import datetime as DateTime
> 
> t = [DateTime(2011,1,day) for day in xrange(1,20)]
> x = [np.nan for i in xrange(1,20)]
> 
> plt.plot(t,x)
> plt.show()

Hi Gerrit,

Thanks for the report, though I'm not sure what you expect to
happen here?

Changing at least one of the elements of x to be something other
than nan does not cause the error.

There is an inconsistency, though, in that plt.plot(x,x) when x
is full of nans does not cause any errors.

best,
-- 
Paul Ivanov
314 address only used for lists,  off-list direct email at:
http://pirsquared.org | GPG/PGP key id: 0x0F3E28F7 

On Fri, 2011-03-25 at 01:08 -0700, Paul Ivanov wrote: 
> Gerrit Kuhlmann, on 2011-03-25 14:26,  wrote:
> > Hi all,
> > 
> > I get a ValueError, if I try to plot a list of numpy.nans against
> > datetime objects. I'm using Python 2.6.5 and Matplotlib 1.0.1 on Ubuntu
> > Linux 10.04. Code and traceback are below.
> > 
> > Best regards,
> > Gerrit
> > 
> > 
> > 
> > Code
> > """"
> > import matplotlib.pyplot as plt
> > import numpy as np
> > from datetime import datetime as DateTime
> > 
> > t = [DateTime(2011,1,day) for day in xrange(1,20)]
> > x = [np.nan for i in xrange(1,20)]
> > 
> > plt.plot(t,x)
> > plt.show()
> 
> Hi Gerrit,
> 
> Thanks for the report, though I'm not sure what you expect to
> happen here?
> 
> Changing at least one of the elements of x to be something other
> than nan does not cause the error.
> 
> There is an inconsistency, though, in that plt.plot(x,x) when x
> is full of nans does not cause any errors.
> 
> best,

Hi Paul,

thanks for your answer. I would expect similar behaviour as for
"plot([0,1,2], [nan,nan,nan])", which creates an empty plot. A passed
through exceptions from the datetime module seems a bit odd. 

Regards,
Gerrit

On Friday, March 25, 2011, Gerrit Kuhlmann
<ger...@st...> wrote:
> On Fri, 2011-03-25 at 01:08 -0700, Paul Ivanov wrote:
>> Gerrit Kuhlmann, on 2011-03-25 14:26,  wrote:
>> > Hi all,
>> >
>> > I get a ValueError, if I try to plot a list of numpy.nans against
>> > datetime objects. I'm using Python 2.6.5 and Matplotlib 1.0.1 on Ubuntu
>> > Linux 10.04. Code and traceback are below.
>> >
>> > Best regards,
>> > Gerrit
>> >
>> >
>> >
>> > Code
>> > """"
>> > import matplotlib.pyplot as plt
>> > import numpy as np
>> > from datetime import datetime as DateTime
>> >
>> > t = [DateTime(2011,1,day) for day in xrange(1,20)]
>> > x = [np.nan for i in xrange(1,20)]
>> >
>> > plt.plot(t,x)
>> > plt.show()
>>
>> Hi Gerrit,
>>
>> Thanks for the report, though I'm not sure what you expect to
>> happen here?
>>
>> Changing at least one of the elements of x to be something other
>> than nan does not cause the error.
>>
>> There is an inconsistency, though, in that plt.plot(x,x) when x
>> is full of nans does not cause any errors.
>>
>> best,
>
> Hi Paul,
>
> thanks for your answer. I would expect similar behaviour as for
> "plot([0,1,2], [nan,nan,nan])", which creates an empty plot. A passed
> through exceptions from the datetime module seems a bit odd.
>
> Regards,
> Gerrit
>

Agreed, I just came across this yesterday while working on my general
exam project.  I have no clue why the behavior would be different
because we are using datetime objects.

Ben Root


>
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All,

This is due to the fact that you have nothing to plot and the axes range
defaults to 0->1.  Unfortunately 0 cannot map to a valid datetime.  I
thought that I had fixed this so that using datetimes would cause the axes
to initialize to a valid datetime value.  Once I get up to speed with the
whole 'git' thing and figure out how to make submissions again, etc. 

A quick work-around is to manually set the  bounds for our datetime axis and
turn off autoscaling until you have some data to display.

I can probably take another look at it, but I am pretty busy and learning
the git model of doing things is only slowing things down.  :(

--James

> -----Original Message-----
> From: Benjamin Root [mailto:ben...@ou...]
> Sent: Friday, March 25, 2011 6:34 AM
> To: Gerrit Kuhlmann
> Cc: mat...@li...
> Subject: Re: [matplotlib-devel] Bug: plot numpy.nans vs. datetime objects
> 
> On Friday, March 25, 2011, Gerrit Kuhlmann
> <ger...@st...> wrote:
> > On Fri, 2011-03-25 at 01:08 -0700, Paul Ivanov wrote:
> >> Gerrit Kuhlmann, on 2011-03-25 14:26,  wrote:
> >> > Hi all,
> >> >
> >> > I get a ValueError, if I try to plot a list of numpy.nans against
> >> > datetime objects. I'm using Python 2.6.5 and Matplotlib 1.0.1 on
> >> > Ubuntu Linux 10.04. Code and traceback are below.
> >> >
> >> > Best regards,
> >> > Gerrit
> >> >
> >> >
> >> >
> >> > Code
> >> > """"
> >> > import matplotlib.pyplot as plt
> >> > import numpy as np
> >> > from datetime import datetime as DateTime
> >> >
> >> > t = [DateTime(2011,1,day) for day in xrange(1,20)] x = [np.nan for
> >> > i in xrange(1,20)]
> >> >
> >> > plt.plot(t,x)
> >> > plt.show()
> >>
> >> Hi Gerrit,
> >>
> >> Thanks for the report, though I'm not sure what you expect to happen
> >> here?
> >>
> >> Changing at least one of the elements of x to be something other than
> >> nan does not cause the error.
> >>
> >> There is an inconsistency, though, in that plt.plot(x,x) when x is
> >> full of nans does not cause any errors.
> >>
> >> best,
> >
> > Hi Paul,
> >
> > thanks for your answer. I would expect similar behaviour as for
> > "plot([0,1,2], [nan,nan,nan])", which creates an empty plot. A passed
> > through exceptions from the datetime module seems a bit odd.
> >
> > Regards,
> > Gerrit
> >
> 
> Agreed, I just came across this yesterday while working on my general exam
> project.  I have no clue why the behavior would be different because we
are
> using datetime objects.
> 
> Ben Root
> 
> 
> >
> > ----------------------------------------------------------------------
> > -------- Enable your software for Intel(R) Active Management
> > Technology to meet the growing manageability and security demands of
> > your customers. Businesses are taking advantage of Intel(R) vPro (TM)
> > technology - will your software be a part of the solution? Download
> > the Intel(R) Manageability Checker today!
> > http://p.sf.net/sfu/intel-dev2devmar
> > _______________________________________________
> > Matplotlib-devel mailing list
> > Mat...@li...
> > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
> >
> 
>
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