matplotlib-users Mailing List for matplotlib

On Monday, November 19, 2012 13:53:21 Eric Firing wrote:

> It is not entirely clear to me what you are trying to do, but it sounds
> like increasing N is not the right way to do it. Three things might help
> you find a better way:
> 
> 1) The colormap is intended to work with a norm that handles the
> translation from your data numbers to the 0-1.0 range used to select
> values from the colormap (with exceptions--see below).  You can choose a
> non-default norm, you can write your own, or you can set the parameters
> (vmin, vmax) of the standard linear norm.
> 
> 2) By creating a colormap and calling its set_under, set_over, and
> set_invalid methods, you can control the colors assigned to data values
> that your norm maps respectively to negative numbers, numbers greater
> than 1, and masked values.  See
> http://matplotlib.org/examples/pylab_examples/contourf_demo.html for an
> example of using set_under and set_over.  See
> http://matplotlib.org/examples/pylab_examples/image_masked.html for
> another example, and for an example of controlling the norm parameters
> or using an alternative norm.
> 
> 3) It is also possible to index directly into the colormap if you use a
> norm that returns an integer data type.  An example of such is the
> BoundaryNorm.
> http://matplotlib.org/examples/pylab_examples/multicolored_line.html
> 
> If all you need is a single assignment of a color to a "large value",
> then using the set_over method will take care of it.
> 
> Eric

Thanks for your answer.

My goal is to keep the correct color, i.e. blue, for the point located at 
(x=0.3, y=0.4), even if there are very large values of z on the plot. As I 
said, increasing N is not satisfying because it leads to large amounts of 
memory to be used. But for the time being, this is the only solution I have 
found.

I cannot use the set_over method to do that, because the "large  value" is not 
the only one. Indeed, what I want to do is an imshow plot, with a colorbar 
containing three different linear portions:
* one portion for the values of z contained between the minimum and maximum 
value of z in some measure points.
* one portion for the values of z below the minimum z in the measure points.
* one portion for the values of z above the maximum z in the measure points.

My problem is that I may have very large values on the plot in the range below 
or above the measures z. So I have exactly the problem shown in my dummy 
example of the previous post: all my measures have the same color, although 
they should not, because I have created a colormap that should handle this 
situation (three different linear portions in the map). The only workaround I 
have found is to increase the value of N, but in my case it has to be very 
large, such that the plot is very slow to display, or even can ask for huge 
amounts of memory.

Thus it seems to me that my dummy example given in the previous post covers 
exactly the problem encountered in my real-world imshow function.

Is there a memory-efficient workaround in my dummy example (instead of 
increasing N)?

Thanks,

TP

2012/11/4 Brickle Macho <bri...@gm...>:
> [...] When I show() a plot form within a Qt application I get the
> following message printed on the console:
>
> QCoreApplication::exec: The event loop is already running
>
> I think I understand the error, obviously the application I calling form
> control the even loop.  I suppose I need to somehow supply a parent
> window to pylab plot or the show() function.   Is there a way to create
> a plot and show so as not to use the main loop?

Do not use show() in a GUI application.
If you have a FigureCanvas instance embedded in your app, call its
draw() method.
If you use pyplot.figure() to create a matplotlib window from your
app, call pyplot.draw().

Goyo

2012/11/22 Jeffrey Melloy <jm...@gm...>:
> I'm graphing data from a web service, and seem to have stumbled upon a
> bug when dates are graphed without any values.
>
> Here's a minimum repro:
>
> import datetime
> import matplotlib.pyplot as plt
>
> fig = plt.figure()
> ax = fig.add_subplot(111)
>
> x = []
> st = datetime.datetime(2012,11,21)
> while st < datetime.datetime(2012,11,21, 16, 00):
>     x.append(st)
>     st = st + datetime.timedelta(minutes=30)
> y = [None] * len(x)
>
> ax.plot(x,y)
> fig.autofmt_xdate()
> plt.show()
>
>
> The stack trace I get:
>
> Traceback (most recent call last):
>   File "min_mpl.py", line 15, in <module>
>     fig.autofmt_xdate()
>   File "c:\python26\lib\site-packages\matplotlib\figure.py", line 318,
> in autofmt_xdate
>     for label in ax.get_xticklabels():
>   File "c:\python26\lib\site-packages\matplotlib\axes.py", line 2507,
> in get_xticklabels
>     self.xaxis.get_ticklabels(minor=minor))
>   File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1104,
> in get_ticklabels
>     return self.get_majorticklabels()
>   File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1088,
> in get_majorticklabels
>     ticks = self.get_major_ticks()
>   File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1186,
> in get_major_ticks
>     numticks = len(self.get_major_locator()())
>   File "c:\python26\lib\site-packages\matplotlib\dates.py", line 749,
> in __call__
>     self.refresh()
>   File "c:\python26\lib\site-packages\matplotlib\dates.py", line 758, in refresh
>     dmin, dmax = self.viewlim_to_dt()
>   File "c:\python26\lib\site-packages\matplotlib\dates.py", line 530,
> in viewlim_to_dt
>     return num2date(vmin, self.tz), num2date(vmax, self.tz)
>   File "c:\python26\lib\site-packages\matplotlib\dates.py", line 289,
> in num2date
>     if not cbook.iterable(x): return _from_ordinalf(x, tz)
>   File "c:\python26\lib\site-packages\matplotlib\dates.py", line 203,
> in _from_ordinalf
>     dt = datetime.datetime.fromordinal(ix)
> ValueError: ordinal must be >= 1
>
> Adding a 0 & the current date stops getting the exception, but the
> range seems wildly messed up. (2011 - 2014).

I can't figure out what's going on here, the calls in the stack trace
seem unrelated to Y data.
As a quick and dirty workaround you can set the first and last Y
values to 0 --won't work well if you use markers.

Goyo

This may help you if I understand your basic problem. I use a lot of
interactive plots. This is an example of the work around to show() that I
use:
 
import matplotlib.pyplot as plt
plt.ion()
fig = plt.figure(figsize=(10,8))
ax = fig.add_axes([.15,.1,.8,.65])
ax.plot([1,2,3])
ax.set_title('Fisrt Plot')
raw_input('Enter to close and Continue: ')
plt.close(fig)

When I use this method when connecting to the axes I re-draw the figure
after updating using:
fig.canvas.draw()
I hope this was useful

Regards,
Bob




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Sent from the matplotlib - users mailing list archive at Nabble.com.

I'm graphing data from a web service, and seem to have stumbled upon a
bug when dates are graphed without any values.

Here's a minimum repro:

import datetime
import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(111)

x = []
st = datetime.datetime(2012,11,21)
while st < datetime.datetime(2012,11,21, 16, 00):
    x.append(st)
    st = st + datetime.timedelta(minutes=30)
y = [None] * len(x)

ax.plot(x,y)
fig.autofmt_xdate()
plt.show()


The stack trace I get:

Traceback (most recent call last):
  File "min_mpl.py", line 15, in <module>
    fig.autofmt_xdate()
  File "c:\python26\lib\site-packages\matplotlib\figure.py", line 318,
in autofmt_xdate
    for label in ax.get_xticklabels():
  File "c:\python26\lib\site-packages\matplotlib\axes.py", line 2507,
in get_xticklabels
    self.xaxis.get_ticklabels(minor=minor))
  File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1104,
in get_ticklabels
    return self.get_majorticklabels()
  File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1088,
in get_majorticklabels
    ticks = self.get_major_ticks()
  File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1186,
in get_major_ticks
    numticks = len(self.get_major_locator()())
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 749,
in __call__
    self.refresh()
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 758, in refresh
    dmin, dmax = self.viewlim_to_dt()
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 530,
in viewlim_to_dt
    return num2date(vmin, self.tz), num2date(vmax, self.tz)
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 289,
in num2date
    if not cbook.iterable(x): return _from_ordinalf(x, tz)
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 203,
in _from_ordinalf
    dt = datetime.datetime.fromordinal(ix)
ValueError: ordinal must be >= 1

Adding a 0 & the current date stops getting the exception, but the
range seems wildly messed up. (2011 - 2014).