pandasで、行 or 列内に欠損値がある時に、無視して加算・無視せず加算する方法 ref: https://qiita.com/kyoro1/items/ce89d6d444eec2b26512

file0.txt

import pandas as pd
import numpy as np

df = pd.DataFrame({'C1': [1, np.nan, np.nan],
                   'C2': [2, 1, 3],
                   'C3': [np.nan, np.nan, 1]})

file1.txt

df
#    C1  C2   C3
#0  1.0   2  NaN
#1  NaN   1  NaN
#2  NaN   3  1.0

file2.txt

df[['C1']].sum(skipna=True)
#C1    1.0
#dtype: float64

file3.txt

df[['C2']].sum(skipna=True)
#C2    6
#dtype: int64

file4.txt

df[['C1']].sum(skipna=False)
#C1   NaN
#dtype: float64

file5.txt

df[['C2']].sum(skipna=False)
#C2    6
#dtype: int64