Counting the occurence of numpy.array object in a list of numpy.array objects

Question

If I have a list:

a = [np.array([1,1,1]), np.array([1,1,1]), np.array([1,1,1])]

How to do something like, a.count(np.array([1,1,1])? This throws:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Is there a function similar to .count()?

What you have in this example is a Python list of numpy objects. — dawg
– dawg, Commented Dec 25, 2019 at 4:17
count is using == teat, which for arrays is element-wise, resulting in the ambiguity error. — hpaulj
– hpaulj, Commented Dec 25, 2019 at 6:05

Austin · Accepted Answer · 2019-12-25 04:18:54Z

1

You can use np.array_equal with sum on generator:

>>> sum(np.array_equal(x, [1,1,1]) for x in a)
3

answered Dec 25, 2019 at 4:18

Austin

26.1k4 gold badges28 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Dima Chubarov · Accepted Answer · 2019-12-25 04:21:25Z

1

Or map np.array_equal and apply count to the result

map(lambda x: np.array_equal(np.array([1,1,1]),x), a).count(True)

answered Dec 25, 2019 at 4:21

Dima Chubarov

17.3k7 gold badges45 silver badges85 bronze badges