[Numpy-discussion] histogram using decending range -- what do the results mean?
Stuart Brorson
sdb@cloud9....
Fri Oct 5 16:32:03 CDT 2007
Guys --
I'm a little puzzled by a NumPy behavior. Perhaps the gurus on this
list can enlighten me, please!
I am working with numpy.histogram. I have a decent understanding of
how it works when given an ascending range to bin into. However, when
I give it a *decending* range, I can't figure out what the results
mean. Here's an example:
------------------------ <session log> --------------------
>>> A = numpy.array([1, 2, 3, 4, 5, 6, 5, 4, 5, 4, 3, 2, 1])
>>> (x, y) = numpy.histogram(A, range=(0, 7))
>>> x
array([0, 2, 2, 0, 2, 3, 0, 3, 1, 0])
>>>
>>> (x, y) = numpy.histogram(A, range=(7, 0))
>>> x
array([ 0, -1, -3, 0, -3, -2, 0, -2, -2, 13])
>>>
-------------------- </session log> ------------------------
Please set aside the natural response "the user shouldn't bin into
a decending range!" since I am trying to figure out what computation
NumPy actually does in this case and I don't want a work-around. And
yes, I have looked at the source. It's nicely vectorized, so I find
the source rather opaque.
Therefore, I would appreciate it if if some kind soul could answer a
couple of questions:
* What does the return mean for range=(7, 0)?
* Why should the return histogram have negative elements?
* If it truely isn't meaningful, why not catch the case and reject
input? Maybe this is a bug.... ???
Thanks!
Stuart
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