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bblay opened this issue Oct 2, 2012 · 4 comments
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append bug : masked array #478

bblay opened this issue Oct 2, 2012 · 4 comments
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00 - Bug component: numpy.lib

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@bblay
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bblay commented Oct 2, 2012

The source data should not be modified by numpy.append:

import numpy, numpy.ma

data = numpy.arange(20).reshape(4,5)
data[:2, :2] = -1
data = numpy.ma.masked_less(data, 0)

print "Before", data.shape, data.mask.shape 
new_array = numpy.append(data, data[:, :1], axis=1)
print "After", data.shape, data.mask.shape

Output:

Before (4, 5) (4, 5)
After (4, 5) (5, 4)

(using v1.6.1)
@bblay bblay mentioned this issue Oct 2, 2012
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@pelson
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pelson commented Oct 2, 2012

Looks like this is fixed on master.

On 1.6.1:

In [1]: import numpy

In [2]: data = numpy.arange(6).reshape(3, 2)

In [3]: data = numpy.ma.masked_greater(data, 0)

In [4]: new_arr = numpy.append(data, data[:, -1:], axis=1)

In [5]: print data.shape
(3, 2)

In [6]: print data.mask
[[False  True  True]
 [ True  True  True]]

In [7]: print data.mask.shape
(2, 3)

In [8]: print new_arr.mask
False

In [9]: print new_arr.shape
(3, 3)

(note that the original data's mask shape has been changed)

In numpy '1.8.0.dev-e18e744':

In [3]: import numpy

In [4]: data = numpy.arange(6).reshape(3, 2)

In [5]: data = numpy.ma.masked_greater(data, 0)

In [6]: new_arr = numpy.append(data, data[:, -1:], axis=1)

In [7]: print data.shape
(3, 2)

In [8]: print data.mask
[[False  True]
 [ True  True]
 [ True  True]]

In [9]: print data.mask.shape
(3, 2)

In [10]: print new_arr.mask
False

In [11]: print new_arr.shape
(3, 3)

It would be nice if new_arr had the appropriate mask, I found a relevant request here: http://projects.scipy.org/numpy/ticket/1623

@numpy-gitbot numpy-gitbot mentioned this issue Oct 19, 2012
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@jjhelmus
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The original issue from @bblay has been fixed for quite some time as indicated by @pelson and is still fixed in the current master. The inappropriate mask issue was dicussed on the numpy mailing list in September 2010. Trac ticket (1623) became GH #2219 and was closed with the addition of ma.append in #4339. I believe with this change this issue can be closed.

@jjhelmus
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As an example of the new behavior

import numpy as np

print np.version.version

data = np.arange(6).reshape(3,2)
data = np.ma.masked_greater(data, 0)
new_arr = np.ma.append(data, data[:, -1:], axis=1)

print "data.shape", data.shape
print "data.mask", data.mask
print "data.mask.shape", data.mask.shape
print "new_arr.mash", new_arr.mask
print "new_arr.mask.shape", new_arr.mask.shape
1.11.0.dev0+941a4e0
data.shape (3, 2)
data.mask [[False  True]
 [ True  True]
 [ True  True]]
data.mask.shape (3, 2)
new_arr.mash [[False  True  True]
 [ True  True  True]
 [ True  True  True]]
new_arr.mask.shape (3, 3)

@charris
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charris commented Sep 28, 2015

OK, thanks for the heads up. Closing.

@charris charris closed this as completed Sep 28, 2015
@pelson pelson mentioned this issue Sep 28, 2015
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@charris @pelson @jjhelmus @bblay