Finding number of zero elements in data

Question

I have the code:

def find_zeros(data):
    '''creates a list of the indexes of the zeros in the data'''
    zeroidx=np.where(np.any(data==0, axis=1))
    print zeroidx
    return len(zeroidx) 

But the result is:

(array([525, 526, 527, 528, 529, 530, 531, 532, 533, 534, 535, 536, 537,
       538, 539, 540, 541, 542, 543, 544, 545, 546, 547, 548, 549, 550,
       551, 552, 553, 554, 555, 556, 557, 558, 559, 560, 561, 562, 563,
       564, 565], dtype=int64),)

which gives the length 1.

How do I find the length of the array of numbers?

This finds the locations of the zeros. Basically I just want to know how many zeros there are in the data? Is there a better way otherwise?

Answer 1

len(data) - numpy.count_nonzero(data)

There's a builtin for this.

Answer 2

Just do check for the zero value and call sum on the resulting boolean array:

(data == 0).sum()

This is a more general solution that can be used for finding any value not just zero and nonzero numbers in the array.

And it even performs slightly but insignificantly better the count_nonzero (the array length is 100000000):

%timeit (a == 0).sum()
1 loops, best of 3: 249 ms per loop

%timeit len(a) - numpy.count_nonzero(a)
1 loops, best of 3: 326 ms per loop