infinite range for hist(histtype="step")

[anntzer]

In [1]: plt.hist(np.arange(10), range=(0, np.inf))
# empty plot
Out[1]: 
(array([ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.]),
 array([ nan,  inf,  inf,  inf,  inf,  inf,  inf,  inf,  inf,  inf,  inf]),
 <a list of 10 Patch objects>)

In [2]: plt.hist(np.arange(10), range=(0, np.inf), histtype="step")
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-2-1921805d8f19> in <module>()
----> 1 plt.hist(np.arange(10), range=(0, np.inf), histtype="step")

/usr/lib/python3.5/site-packages/matplotlib/pyplot.py in hist(x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, hold, **kwargs)
   2894                       histtype=histtype, align=align, orientation=orientation,
   2895                       rwidth=rwidth, log=log, color=color, label=label,
-> 2896                       stacked=stacked, **kwargs)
   2897         draw_if_interactive()
   2898     finally:

/usr/lib/python3.5/site-packages/matplotlib/axes/_axes.py in hist(self, x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, **kwargs)
   5872                         ymin = np.amin(m[m != 0])
   5873                         # filter out the 0 height bins
-> 5874                 ymin = max(ymin*0.9, minimum)
   5875                 ymin = min(ymin0, ymin)
   5876                 self.dataLim.intervaly = (ymin, ymax)

UnboundLocalError: local variable 'ymin' referenced before assignment

Obviously there's isn't much to do here other than improving the error reporting in the second case.

[lzkelley]

Should the first case raise an error as-well? i.e. perhaps hist should assert that the range is finite.

(Aside: there's no error in the second case in python2.x)

[anntzer]

I think it should.

[tacaswell]

This should go as a bug against numpy. We delegate all of the histogram computation to them, we should not maintain significant validation on top of that.

[anntzer]

Actually this behavior has changed recently, probably with numpy 1.10 & matplotlib 1.5: now neither command raises an error, and both give an empty plot.

[lzkelley]

I've brought this up in the numpy-discussion mailing list. Should we close this issue and punt it to them?

[tacaswell]

Yes, closing this here. Please ping to have re-opened if discussions with numpy go very badly. If you end up creating an issue/PR over at numpy can you please also link to this issue?

[heroxbd]

@lzkelley Could you please provide a reference to the topic at numpy-discussion mailing list?

[lzkelley]

Sure, the this is the topic which I opened (no replies). And this is the PR I put in to numpy (which was merged).

[heroxbd]

I do think it is a bug of matplotlib.
My system is with python-2.7.10, numpy-1.10.4 and matplotlib-1.5.1.

from matplotlib import pylab as plt
plt.hist([1,3], range(1,2)) # success
plt.hist([1,3], range(1,3), histtype="step") # success
plt.hist([1,3], range(1,2), histtype="step") # exception

UnboundLocalError                         Traceback (most recent call last)
<ipython-input-6-73c33d0106be> in <module>()
----> 1 plt.hist([1,3], range(1,2), histtype="step")

/disk/usr100/gentoo/usr/lib64/python2.7/site-packages/matplotlib/pyplot.pyc in hist(x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, hold, data, **kwargs)
   2956                       histtype=histtype, align=align, orientation=orientation,
   2957                       rwidth=rwidth, log=log, color=color, label=label,
-> 2958                       stacked=stacked, data=data, **kwargs)
   2959     finally:
   2960         ax.hold(washold)

/disk/usr100/gentoo/usr/lib64/python2.7/site-packages/matplotlib/__init__.pyc in inner(ax, *args, **kwargs)
   1810                     warnings.warn(msg % (label_namer, func.__name__),
   1811                                   RuntimeWarning, stacklevel=2)
-> 1812             return func(ax, *args, **kwargs)
   1813         pre_doc = inner.__doc__
   1814         if pre_doc is None:

/disk/usr100/gentoo/usr/lib64/python2.7/site-packages/matplotlib/axes/_axes.pyc in hist(self, x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, **kwargs)
   6207                         ymin = np.amin(m[m != 0])
   6208                         # filter out the 0 height bins
-> 6209                 ymin = max(ymin*0.9, minimum) if not input_empty else minimum
   6210                 ymin = min(ymin0, ymin)
   6211                 self.dataLim.intervaly = (ymin, ymax)

UnboundLocalError: local variable 'ymin' referenced before assignment

[heroxbd]

Thanks @lzkelley. This bug is not caused by infinite numbers, but histogram input failing outside of the specified range.

[lzkelley]

@heroxbd I see - yeah, this looks like a slightly different issue - but hopefully a similar fix. That is really strange: I see that plt.hist([1,3], 1, histtype="step") works fine....