Finding substring in pandas frozenset

问题

I'm trying to find a substring in a frozenset, however I'm a bit out of options.

My data structure is a pandas.dataframe (it's from the association_rules from the mlxtend package if you are familiar with that one) and I want to print all the rows where the antecedents (which is a frozenset) include a specific string.

Sample data:

    print(rules[rules["antecedents"].str.contains('line', regex=False)])

However whenever I run it, I get an Empty Dataframe.

When I try running only the inner function on my series of rules["antecedents"], I get only False values for all entries. But why is that?

回答1:

Because dataframe.str.* functions are for string data only. Since your data is not string, it will always be NaN regardless the string representation of it. To prove:

>>> x = pd.DataFrame(np.random.randn(2, 5)).astype("object")
>>> x
         0         1         2          3          4
0 -1.17191  -1.92926 -0.831576 -0.0814279   0.099612
1 -1.55183 -0.494855   1.14398   -1.72675 -0.0390948
>>> x[0].str.contains("-1")
0   NaN
1   NaN
Name: 0, dtype: float64

What can you do:

Use apply:

>>> x[0].apply(lambda x: "-1" in str(x))
0    True
1    True
Name: 0, dtype: bool

So your code should write:

print(rules[rules["antecedents"].apply(lambda x: 'line' in str(x))])

You might want to use 'line' in x if you mean an exact match on element

来源：https://stackoverflow.com/questions/55402544/finding-substring-in-pandas-frozenset