only integers, slices (`:`), ellipsis (`...`), numpy.newaxis (`None`) and integer or boolean arrays are valid indices

Question

I am implementing fft as part of my homework. My problem lies in the implemention of shuffling data elements using bit reversal. I get the following warning:

DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future.

data[x], data[y] = data[y], data[x]

And the auto grading system (provided by university) returns the following:

error: only integers, slices (:), ellipsis (...), numpy.newaxis (None) and integer or boolean arrays are valid indices.

My code is:

def shuffle_bit_reversed_order(data: np.ndarray) -> np.ndarray:
    """
    Shuffle elements of data using bit reversal of list index.

    Arguments:
    data: data to be transformed (shape=(n,), dtype='float64')

    Return:
    data: shuffled data array
    """

    # implement shuffling by reversing index bits

    size = data.size

    half = size/2;

    for x in range(size):
        xx = np.int(x)
        n = np.int(half)

        y = 0

        while n > 0:
            y += n * np.mod(xx,2)
            n /= 2
            xx = np.int(xx /2)

        if (y > x):

            data[x], data[y] = data[y], data[x]

    return data

I have already implemented the function for fft but it won't work until I get this shuffling function working. I think the problem is my data is of type 'float64' and I may have used it as an integer but I don't know how I can solve it.

Answer 1

I believe your problem is this: in your while loop, n is divided by 2, but never cast as an integer again, so it becomes a float at some point. It is then added onto y, which is then a float too, and that gives you the warning.