On Sun, Nov 7, 2010 at 9:40 AM, LB <bravo.l...@gmail.com> wrote:
> Hi,
>
> I'm trying to draw a bar chart according to
> http://matplotlib.sourceforge.net/examples/api/barchart_demo.html, and I'm
> having to difficulties :
>
> - when the first bar has a zero height, it is no taken into account during
> the axis limits calculation and is not visible
>
> - texts objects can exceed chart area and collide with the chart title.
>
> Is there a way to calculate the axis limit to use to include all texts
> objects into the chart area ?
>
> Here is the code I used :
>
> [code]
> #!/usr/bin/env python
>
> import numpy as np
> import matplotlib.pyplot as plt
>
> menMeans = [ 0. , 998. , 1210. , 1449. ,
> 1496. , 1493. , 1593.40002441, 1517.5 ]
>
> ind = np.arange(len(menMeans)) # the x locations for the groups
> width = 0.8 # the width of the bars
>
> fig = plt.figure()
> ax = fig.add_subplot(111)
> rects1 = ax.bar(ind, menMeans, width, color='r')
>
> # add some
> ax.set_ylabel('Scores')
> ax.set_title('A very very long title for testing.')
>
> def autolabel(rects):
> # attach some text labels
> for rect in rects:
> height = rect.get_height()
> ax.text(rect.get_x()+rect.get_width()/2., 1.05*height,
> '%d'%int(height),
> ha='center', va='bottom')
>
> autolabel(rects1)
>
> plt.show()
> [/code]
>
> Best regards,
>
> --
> LB
>
>
LB,
I can confirm the problem with zero height bars not being included in the
determination of the axes limits.
As for the text getting too high, this is something that many users have
noticed in a variety of different scenarios. Part of the problem is that it
is perfectly valid to have text outside the axes area, or straddling it, and
that we have yet to come up with a decent way to handle this properly.
Imagine, for example, contour labels near an axes edge. I certainly would
not like to have the text labels to force the axes limits to change just to
fit the text (I would rather it be clipped). Then again, your use-case is
an example where auto resizing makes sense.
The other issue is that it is impossible to know (in a general sense) a
priori the extent of a given text object before rendering (although I think
there might be some code in text.py to address this, but it might be
assuming that the object has been rendered already). The particular
sticking point is LaTeX strings.
Therefore, rather than design a layout engine for all of matplotlib, it has
become standard practice to make it easy to adjust the plot parameters
programatically to deal with situations like this. For example, in your
use-case, you know what the maximum bar height will be, and you know roughly
how high the text will be from previous runs. You could then set the y
limits to pad a certain amount on top of the maximum bar height to make sure
you have enough clearance.
I hope that helps, and I will take a peek at the zero-height bar issue as
well.
Ben Root
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