I need to find the indicies of both the zero and nonzero elements of an array.

Put another way, I want to find the complementary indices from numpy.nonzero().

The way that I know to do this is as follows:

indices_zero = numpy.nonzero(array == 0)
indices_nonzero = numpy.nonzero(array != 0)

This however means searching the array twice, which for large arrays is not efficient. Is there an efficient way to do this using numpy?

Assuming you already have the range for use numpy.arange(len(array)), just get and store the logical indices:

bindices_zero = (array == 0)

then when you actually need the integer indices you can do

indices_zero = numpy.arange(len(array))[bindices_zero]

or

indices_nonzero = numpy.arange(len(array))[~bindices_zero]