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pandaschaining

Pandas Series Chaining: Filter on boolean value

How can I filter a pandas series based on boolean values?

Currently I have:

s.apply(lambda x: myfunc(x, myparam).where(lambda x: x).dropna()

What I want is only keep entries where myfunc returns true.myfunc is complex function using 3rd party code and operates only on individual elements.

How can i make this more understandable?

Solution

  • Use boolean indexing:

    mask = s.apply(lambda x: myfunc(x, myparam))
print (s[mask])

    If also is changed index values in mask filter by 1d array:

    #pandas 0.24+
print (s[mask.to_numpy()])

#pandas below
print (s[mask.values])

    EDIT:

    s = pd.Series([1,2,3])

def myfunc(x, n):
    return x > n

myparam = 1
a = s[s.apply(lambda x: myfunc(x, myparam))]
print (a)
1    2
2    3
dtype: int64

    Solution with callable is possible, but a bit overcomplicated in my opinion:

    a = s.loc[lambda s: s.apply(lambda x: myfunc(x, myparam))]
print (a)
1    2
2    3
dtype: int64