# [Numpy-tickets] [NumPy] #586: (Retry) Patch to detect max < min in histogram(X, range)

NumPy numpy-tickets@scipy....
Thu Oct 18 23:19:44 CDT 2007

```#586: (Retry) Patch to detect max < min in histogram(X, range)
-------------------------+--------------------------------------------------
Reporter:  brorson      |        Owner:  somebody
Type:  enhancement  |       Status:  new
Priority:  normal       |    Milestone:  1.0.4
Component:  numpy.lib    |      Version:  none
Severity:  normal       |   Resolution:
Keywords:               |
-------------------------+--------------------------------------------------
Comment (by jarrod.millman):

Robert Kern's response to Stuart Brorson's original email follows:

> 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:
{{{
>>> 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])
}}}
> 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)?

Nothing.

> *  Why should the return histogram have negative elements?

Because there are subtractions involved that depend on the bins being
increasing
which they are not if the given range is incorrect.

> *  If it truely isn't meaningful, why not catch the case and reject
> input?  Maybe this is a bug....  ???

Patches are welcome.

--
Ticket URL: <http://scipy.org/scipy/numpy/ticket/586#comment:2>
NumPy <http://projects.scipy.org/scipy/numpy>
The fundamental package needed for scientific computing with Python.
```

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