Caution when you apply
all on a one-column Boolean DataFrame, or you should never apply these 2 functions to such a DataFrame because it works differently from your intention.
The logics of
def all(iterable): for element in iterable: if not element: return False return True
def any(iterable): for element in iterable: if element: return True return False
The trickiest part with a DataFrame is that when being iterated, its
elements are actually its column names, with types!
A column name can be a string (in most cases), an integer (acceptable) or even a Boolean (What?). Therefore when applying
all() to a DataFrame, you’re actually iterating its column names, which are then evaluated in the
if element: clause, and at the same time NONE of the values underneath is accessed at all.
>>> foo = pd.DataFrame(data=[1,2]) >>> foo 0 0 1 1 2 >>> for element in foo: ... print(element) ... 0
>>> foo = pd.DataFrame(data=[1,2], columns=[True]) >>> foo True 0 1 1 2 >>> for element in foo: ... print(element) ... True
And this exactly explains the seemingly contradicting results in the following code:
>>> one_c_df = pd.DataFrame(data=[False, False], index=["a", "b"], columns=["a_colname_not_evaluated_to_False"]) >>> one_c_df a_colname_not_evaluated_to_False a False b False >>> any(one_c_df) # I cannot believe this at first sight! True >>> all(one_c_df) True
>>> series = pd.Series(data=[False, False], index=["a", "b"], name="does_not_matter") >>> series a False b False Name: does_not_matter, dtype: bool >>> any(series) False >>> all(series) False
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