Dear all numpy users,
I am using numpy 1.6.1
I find that if you want to change some member values in a masked array
according to some conditional selection.
suppose a is a masked array, you want to change all value below zero to
zero.
you must always use
a[np.nonzero(a<0)]=0
rather than a[a<0]=0.
the latter will lose all masked elements.
an example:
In [24]: a=np.arange(10.)
In [25]: a=np.ma.masked_array(a,mask=a<3)
In [28]: a[a<5]=2.
In [29]: a
Out[29]:
masked_array(data = [2.0 2.0 2.0 2.0 2.0 5.0 6.0 7.0 8.0 9.0],
mask = [False False False False False False False False False
False],
fill_value = 1e+20)
In [30]: b=np.arange(10.)
In [31]: b=np.ma.masked_array(b,mask=b<3)
In [34]: b[np.nonzero(b<5)]=2.
In [35]: b
Out[35]:
masked_array(data = [-- -- -- 2.0 2.0 5.0 6.0 7.0 8.0 9.0],
mask = [ True True True False False False False False False
False],
fill_value = 1e+20)
cheers,
Chao
--
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Chao YUE
Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL)
UMR 1572 CEA-CNRS-UVSQ
Batiment 712 - Pe 119
91191 GIF Sur YVETTE Cedex
Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16
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