8000 IndexError on apply_along_axis with empty 2D array · Issue #7454 · numpy/numpy · GitHub
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IndexError on apply_along_axis with empty 2D array #7454

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Wilfred opened this issue Mar 23, 2016 · 3 comments
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IndexError on apply_along_axis with empty 2D array #7454

Wilfred opened this issue Mar 23, 2016 · 3 comments

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@Wilfred
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Wilfred commented Mar 23, 2016 
In [21]: a = np.empty(shape=(0,0))

In [22]: np.lib.apply_along_axis(sum, 1, a)
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-22-2fcce4e707fd> in <module>()
----> 1 np.lib.apply_along_axis(sum, 1, a)

myvirtualenv/lib/python2.7/site-packages/numpy-1.9.2-py2.7-linux-x86_64.egg/numpy/lib/shape_base.pyc in apply_along_axis(func1d, axis, arr, *args, **kwargs)
     89     outshape = asarray(arr.shape).take(indlist)
     90     i.put(indlist, ind)
---> 91     res = func1d(arr[tuple(i.tolist())], *args, **kwargs)
     92     #  if res is a number, then we have a smaller output array
     93     if isscalar(res):

IndexError: index 0 is out of bounds for axis 0 with size 0
@eric-wieser
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eric-wieser commented Feb 13, 2017 •
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What do you think the correct behaviour here is? It's impossible to know what dtype of value to return without invoking the function. So should we invoke the function on an array of garbage?

As of #8441, this now raises StopIteration instead, which is even worse, as it could cause silent failures in iterator

@eric-wieser eric-wieser mentioned this issue Feb 13, 2017
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@Wilfred
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Wilfred commented Feb 13, 2017

I was going to suggest asserting that the array was non-empty, but I see #8614 is raising ValueError which seems like a clean solution to me.

I think I bumped into this when testing boundary cases in code that wraps apply_along_axis.

@eric-wieser
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Also, this duplicates #6927

@mhvk mhvk closed this as completed in 61640a8 Feb 18, 2017
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