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pythonarraysnumpyfill

Fill specific values of a numpy array (master) with values from another numpy array (slave) from same index position

I prepared a mini example for my question. Assume we have a master numpy array

master = 
array([[-1, -1, -1,  2,  2,  2],
       [-1, -1, -1,  2,  2,  2],
       [-1, -1, -1,  2,  2,  2],
       [ 2,  2,  2, -1, -1, -1],
       [ 2,  2,  2, -1, -1, -1],
       [ 2,  2,  2, -1, -1, -1]])

Secondly we have a slave numpy array with the exact same shape:

slave=
array([[-1, -1, -1,  3,  3,  3],
       [-1, -1, -1,  3,  3,  3],
       [-1, -1, -1,  3,  3,  3],
       [ 3,  3,  3,  3,  3,  3],
       [ 3,  3,  3,  3,  3,  3],
       [ 3,  3,  3,  3,  3,  3]])

What I'm looking for is the following: result = fill master array with slave values where master = -1

result=
array([[-1, -1, -1,  2,  2,  2],
       [-1, -1, -1,  2,  2,  2],
       [-1, -1, -1,  2,  2,  2],
       [ 2,  2,  2,  3,  3,  3],
       [ 2,  2,  2,  3,  3,  3],
       [ 2,  2,  2,  3,  3,  3]])

In my real world scenario I have dozens of arrays with more than 12 million values each and they all have nodata values on different places. I want to fill the master array with the other arrays, where master values are nodata.

I really searched and tried a lot, like extract boolean masks but I really do not know how to fill on the exact same index coordinates without iterating over all single cells.

Would be great if I get help from you...

Solution

  • Use:

    result = np.where(master == -1, slave, master)