Masked Arrays

Masked arrays are arrays with invalid or missing values. Numpy has numpy.ma module dedicated to masked arrays.

np.ma.array([1, 2, 3, 4], mask=[0, 1, 0, 1])
# masked_array(data=[1, --, 3, --],
#            mask=[False,  True, False,  True],
#      fill_value=999999)

References

1. https://lectures.scientific-python.org/intro/numpy/elaborate_arrays.html#maskedarray-dealing-with-propagation-of-missing-data