How to update a numpy array based on a masked array w/ same dimension and shape

Question

I have two arrays with same dimension and shape. this nv_arr array has null values (-9999). I've created a masked array nv_mask to mask all values besides -9999 to somehow "update" this out array by the position, without the need to create a new array.

In other words, numbers 0, 3, 6 and 2 must be replaced by -9999. How can I do that?

    >>> nv_arr
     ([[-9999,   123,   -9999],
       [-9999,   444,   444],
       [-9999,   323,   323]])

>>> nv_mask
[[-9999 -- -9999]
 [-9999 -- --]
 [-9999 -- --]]

 >>> out
      ([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])

cs95 · Accepted Answer · 2018-12-19 19:43:23Z

1

Assuming nv_mask is a MaskedArray, you can call the .mask attribute to set values:

>>> out[~nv_mask.mask] = -9999
>>> out 
array([[-9999,     1, -9999],
       [-9999,     4,     5],
       [-9999,     7,     8]])

edited Dec 19, 2018 at 19:43

answered Dec 19, 2018 at 18:52

cs95

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2 Comments

Paul Panzer Over a year ago

Almost correct ;-P .mask is True at the masked values, not the valid ones.

cs95 Over a year ago

@PaulPanzer Ah, I see I botched up the initialisation of these arrays, so my answer needed a ~ it didn't have. Ty!

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