What to do when Unalignable boolean Series provided as indexer

Event: I was angry when I tried to extract data with a non-NaN index with notna

--Environment --macOS Catalina version 10.15.7 - Python 3.8.5 - pandas 1.1.3

import pandas

if __name__ == '__main__':
    df = pandas.read_csv('CSV.csv')
    print(df[df.query('name== "Ponsuke"')['start'].notna()])

Error message


pandas.core.indexing.IndexingError: Unalignable boolean Series provided as indexer (index of the boolean Series and of the indexed object do not match).

Cause unknown

Because the index of the index of the DataFrame you are trying to extract is not in the result of notna? I want someone to tell me.

#The index of the DataFrame you are trying to extract is 0~There are 40 up to 39
print(df)
#Name Count Start End
#0 Ponsuke 1 9:00  18:00
# ...abridgement...
#39 Ponsuke 10 NaN NaN

#The index of the result of notna is full of missing numbers and only 10
print(df.query('name== "Ponsuke"')['start'].notna())
# 0      True
# 2      True
# 5      True
# 11     True
# 14    False
# 21     True
# 24     True
# 29    False
# 34     True
# 39    False
# Name:start, dtype: bool

If you extract from a DataFrame that matches the index of the result of notna, it seems quite so

#DataFrame that fits the index of the result of notna
print(df.query('name== "Ponsuke"'))
#Name Count Start End
#0 Ponsuke 1 9:00  18:00
#2 Ponsuke 3 9:00  13:00
#5 Ponsuke 7 12:00    NaN
#11 Ponsuke 5 9:00    NaN
#14 Ponsuke 4 NaN NaN
#21 Ponsuke 2 18:00    NaN
#24 Ponsuke 6 18:00    NaN
#29 Ponsuke 9 NaN 18:00
#34 Ponsuke 8 12:00    NaN
#39 Ponsuke 10 NaN NaN

Action: Extract from DataFrame that matches the index of the result of notna

import pandas

if __name__ == '__main__':
    df = pandas.read_csv('CSV.csv')
    ponsuke = df.query('name== "Ponsuke"')
    print(ponsuke[ponsuke['start'].notna()])

did it


Name Count Start End
0 Ponsuke 1 9:00  18:00
2 Ponsuke 3 9:00  13:00
5 Ponsuke 7 12:00    NaN
11 Ponsuke 5 9:00    NaN
21 Ponsuke 2 18:00    NaN
24 Ponsuke 6 18:00    NaN
34 Ponsuke 8 12:00    NaN

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