10000 histogram2d and histogramdd always return a float array · Issue #7845 · numpy/numpy · GitHub
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mnmelo opened this issue Jul 18, 2016 · 5 comments
Open

histogram2d and histogramdd always return a float array #7845

mnmelo opened this issue Jul 18, 2016 · 5 comments
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00 - Bug 54 - Needs decision component: numpy.lib

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@mnmelo
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mnmelo commented Jul 18, 2016

When no normalization is performed the histogram*d functions should return an int array, just as histogram does. A float array is returned instead.

The docs of histogram2d don't mention anything about return type, but also don't follow the style of the docs of histogram, in which it is stated that semantics depend on normalization (I guess this could be written more explicitly). histogramdd does follow the doc style of histogram, but also returns a float array, like histogram2d does.

Running NumPy 1.11.0 on Ubuntu 14.04
Sample code:

arr = np.random.random((20))

## 1D
np.histogram(arr)[0]
Out: array([5, 1, 1, 1, 2, 1, 2, 1, 2, 4])

## 2D
np.histogram2d(arr,arr)[0]
Out: 
array([[ 5.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  1.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  1.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  1.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  2.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  1.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  2.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  1.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  2.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  4.]])

## N-D
np.histogramdd(arr[:,None])[0]
Out: array([ 5.,  1.,  1.,  1.,  2.,  1.,  2.,  1.,  2.,  4.])
#
np.histogramdd(np.column_stack((arr, arr)))[0]
Out: 
array([[ 5.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  1.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  1.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  1.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  2.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  1.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  2.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  1.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  2.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  4.]])
@mnmelo
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mnmelo commented Jul 18, 2016

This would be one more aspect to consolidate across histogram, histogram2d, and histogramdd, as per #4521.

@tom-bird
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tom-bird commented Aug 1, 2016

Yes agreed, I will bring histogram2d and histogramdd in line with histogram

tom-bird added a commit to tom-bird/numpy that referenced this issue Aug 1, 2016
@tom-bird
ENH: numpy#7845. histogram2d and histogramdd return int array when re…
40d7d52 
…levant, in line with histogram
This was referenced Apr 9, 2018
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@tom-bird tom-bird mentioned this issue Apr 10, 2018
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@eric-wieser
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Channeling @charris:

I think this should be discussed on the mailing list as it changes the behavior of the affected functions.

If we decide to go ahead with the change, the fix is simply to remove

numpy/numpy/lib/histograms.py

Lines 937 to 938 in cc1107e

# This preserves the (bad) behavior observed in gh-7845, for now.
hist = hist.astype(float, casting='safe')

@eric-wieser
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Posted to the list at http://numpy-discussion.10968.n7.nabble.com/Changing-the-return-type-of-np-histogramdd-tt45429.html

@eric-wieser eric-wieser mentioned this issue May 1, 2018
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@henryiii henryiii mentioned this issue Nov 2, 2018
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@BvB93 BvB93 mentioned this issue Oct 7, 2021
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@WarrenWeckesser
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The mailing list link given above is dead. I think this is the correct thread: https://mail.python.org/archives/list/numpy-discussion@python.org/thread/NIHE7UT4SDPU6KCDSMUIU2UA52PDSEIJ/

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