从DataFrame提取熊猫系列的非空部分

Question

Say I have this DataFrame:

    C1    C2    C3
0    1   4.4    99
1    2   4.5   200
2    3   NaN    65
3    4   3.2   140

I want to extract only the column (series) C2 and only the non-null elements of that series.

I can do that in two steps:

d = df.loc[df['C2'].notnull()]
s=d['C2']

s will be

0    4.4
1    4.5
3    3.2

Can I do this in one step?

Answer 1

You are talking about dropna

df.C2.dropna()
Out[486]: 
0    4.4
1    4.5
3    3.2
Name: C2, dtype: float64

Answer 2

Consider using query with .notna if you want to filter your dataframe:

df.query('C2.notna()')

Output

   C1   C2   C3
0   1  4.4   99
1   2  4.5  200
3   4  3.2  140

Answer 3

您也可以将两个步骤组合为一个步骤并放下位置

df[df['C2'].notnull()]['C2']