[SciPy-User] pylab

[Joshua Holbrook]

2010/7/19 பழநி சே <palaniappan.chetty at gmail.com>:
> hi,
> I have a question about pylab/matplotlib, I am interested in plots and
> I want to know if I can have some data points in a data sets missing
> but still create a plot using pylab? For example (assuming all modules
> have been imported)
>
>>x = [1,2,3,4]
>>y=[10,20,30,40]
>>pylab.plot(x,y)
>>pylab.show()
>
> works fine. But what if I have one or more data points missing in my y
> data set? like this
>
>>x = [1,2,3,4]
>>y=[10,20, ,40]
>>pylab.plot(x,y)
>>pylab.show()
> I know that I cannot have an empty element in my list and this does not work
>
> Thanks
> --
> Palani
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Hey Palani,

I'm not extremely familiar with matplotlib, but my experience tells me
that, while MPL itself wouldn't really have any nice way to do this,
that you could import a dataset and use python/numpy to clean it up.
For example, you could maybe use filter() and zip()  (zip's my
favorite toy), maybe like this:


    In [30]: x
    Out[30]: [0, 1, 2, 3, 4]

    In [31]: y
    Out[31]: [0, 1, 4, None, 16]

    In [32]: zip(*filter(lambda x: x[1] != None, zip(x,y)))
    Out[32]: [(0, 1, 2, 4), (0, 1, 4, 16)]

and then you could do plot(_[0],_[1]).  Alternately, and this would
probably be worth investigating for bigger datasets, you could maybe
use masked arrays
(http://docs.scipy.org/doc/numpy/reference/maskedarray.baseclass.html)
to do something similar in spirit.

Hope that helped!

--Josh