How do I remove all zero elements from a NumPy array?

Question

I have a rank-1 numpy.array of which I want to make a boxplot. However, I want to exclude all values equal to zero in the array. Currently, I solved this by loo

Answer 1

You can index with a Boolean array. For a NumPy array A:

res = A[A != 0]

You can use Boolean array indexing as above, bool type conversion, np.nonzero, or np.where. Here's some performance benchmarking:

# Python 3.7, NumPy 1.14.3

np.random.seed(0)

A = np.random.randint(0, 5, 10**8)

%timeit A[A != 0]          # 768 ms
%timeit A[A.astype(bool)]  # 781 ms
%timeit A[np.nonzero(A)]   # 1.49 s
%timeit A[np.where(A)]     # 1.58 s