Given the X numpy array, return True if any of its elements is zero

Question

X is given as below:

X = np.array([-1, 2, 0, -4, 5, 6, 0, 0, -9, 10])

My answer is: any(X==0).
But the standard answer is X.any(), and it returns True, which confuses me.

For me, X.any() is looking for if there is any True or 1 in the array. In this case, since there is no 1 in the given X array, it should have returned False. What did I get wrong? Thank you in advance!

"X.any() is looking for if there is any True or 1 in the array" - please RTM: numpy.org/doc/stable/reference/generated/numpy.any.html — ForceBru
– ForceBru, Commented May 23, 2022 at 11:57
Python and numpy see "truthy" values as true. "Truthy" means among other things all int values except 0. — Michael Butscher
– Michael Butscher, Commented May 23, 2022 at 11:59
@ForceBru I read this before, but I misunderstood what truthy value is. By the way, can you kindly explain what RTM is? I googled it but didn't find a likey definition. Thanks! — union77
– union77, Commented May 24, 2022 at 2:12
@ericzheng0404, RTM stands for "Read The Manual". Doing so often helps get the definitions straight: like what a "truthy" value is or what X.any actually does. — ForceBru
– ForceBru, Commented May 24, 2022 at 7:36

mozway · Accepted Answer · 2022-05-23 12:12:46Z

1

X.any() is an incorrect answer, it would fail on X = np.array([0]) for instance (incorrectly returning False).

A correct answer would be: ~X.all(). According to De Morgan's laws, ANY element is 0 is equivalent to NOT (ALL elements are (NOT 0)).

How does it work?

Numpy is doing a implicit conversion to boolean:

X = np.array([-1, 2, 0, -4, 5, 6, 0, 0, -9, 10])
# array([-1, 2, 0, -4, 5, 6, 0, 0, -9, 10])

# convert to boolean
# 0 is False, all other numbers are True
X.astype(bool)
# array([ True,  True, False,  True,  True,  True, False, False,  True, True])

# are all values truthy (not 0 in this case)?
X.astype(bool).all()
# False

# get the boolean NOT
~X.astype(bool).all()
# True

answered May 23, 2022 at 12:12

mozway

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2 Comments

union77 Over a year ago

I think your answer is a better one. By the way, does my answer any(X==0) make sense? I didn't see similar syntax used in manual examples, but it worked in this case. So, I'm wondering is it also a valid answer?

mozway Over a year ago

It works but this is pure python while (X==0).any() is vectorized. I would probably use (X==0).any() in a project as it is much more explicit than ~X.all()

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