[Numpy-discussion] easy way to change part of only unmasked elements value?

[Chao YUE]

Dear Richard,

this is what I want. Thanks!

Chao

On Tue, Sep 11, 2012 at 3:19 PM, Richard Hattersley
<rhattersley at gmail.com>wrote:

> Hi Chao,
>
> If you don't mind modifying masked values, then if you write to the
> underlying ndarray it won't touch the mask:
>
> >>> a = np.ma.masked_less(np.arange(10),5)
> >>> a.base[3:6] = 1
> >>> a
>
> masked_array(data = [-- -- -- -- -- 1 6 7 8 9],
>              mask = [ True  True  True  True  True False False False False
> False],
>        fill_value = 999999)
>
> Regards,
> Richard Hattersley
>
>
> On 10 September 2012 17:43, Chao YUE <chaoyuejoy at gmail.com> wrote:
>
>> Dear all numpy users,
>>
>> what's the easy way if I just want to change part of the unmasked array
>> elements into another new value? like an example below:
>> in my real case, I would like to change a subgrid of a masked numpy array
>> to another value, but this grid include both masked and unmasked data.
>> If I do a simple array[index1:index2, index3:index4] = another_value,
>> those data with original True mask will change into False. I am using numpy
>> 1.6.2.
>> Thanks for any ideas.
>>
>> In [91]: a = np.ma.masked_less(np.arange(10),5)
>>
>> In [92]: or_mask = a.mask.copy()
>> In [93]: a
>> Out[93]:
>> masked_array(data = [-- -- -- -- -- 5 6 7 8 9],
>>              mask = [ True  True  True  True  True False False False
>> False False],
>>        fill_value = 999999)
>>
>>
>> In [94]: a[3:6]=1
>>
>> In [95]: a
>> Out[95]:
>> masked_array(data = [-- -- -- 1 1 1 6 7 8 9],
>>              mask = [ True  True  True False False False False False
>> False False],
>>        fill_value = 999999)
>>
>>
>> In [96]: a = np.ma.masked_array(a,mask=or_mask)
>>
>> In [97]: a
>> Out[97]:
>> masked_array(data = [-- -- -- -- -- 1 6 7 8 9],
>>              mask = [ True  True  True  True  True False False False
>> False False],
>>        fill_value = 999999)
>>
>> Chao
>>
>> --
>>
>> ***********************************************************************************
>> 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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>>
>>
>
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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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