[英]fillna by referring another column but copy same column value using pandas
I have a dataframe like as shown below我有一个 dataframe 如下图所示
df = pd.DataFrame(
{'sub_code' : [np.nan, 'CSE01', np.nan,
'CSE02', 'CSE03', 'CSE02',
'CSE03', 'CSE02'],
'stud_level' : [101, 101, 101, 101,
101, 101, 101, 101],
'grade' : ['STA','STA','PSA','STA','STA','SSA','PSA','QSA']})
I would like to do the below我想做以下
a) Fill NA's in sub_code
column by referring grade
column. a) 通过参考
grade
列在sub_code
列中填写 NA。
b) For ex: grade STA
has corresponding sub_code
non-NA values in row 1,3 and 4
( row 0 has NA value
) b)例如:等级
STA
在row 1,3 and 4
行具有相应的sub_code
非 NA 值( row 0 has NA value
)
c) Copy the very 1st non-NA ( CSE01
) value from grade
column and put it in sub_code
column ( row 0
) c) 从
grade
列复制第一个非 NA ( CSE01
) 值并将其放入sub_code
列 ( row 0
)
I tried the below我尝试了以下
m = df['sub_code'].isna()
df.loc[m, 'sub_code'] = np.where(df.loc[m, 'grade'].ne(np.nan), df['sub_code'], 'not filled')
I expect my output to be like as below我希望我的 output 如下所示
groupby
"grade" and use first
to get the first non-NaN sub_code in each grade. groupby
"grade" 并使用first
获取每个等级中的第一个非 NaN 子代码。 Then use np.where
to fill NaN values in "sub_code":然后使用
np.where
填充“sub_code”中的 NaN 值:
mapper = df.groupby('grade')['sub_code'].first()
df['sub_code'] = np.where(df['sub_code'].isna(), df['grade'].map(mapper), df['sub_code'])
or instead of the second line, you can also use fillna
:或者代替第二行,您也可以使用
fillna
:
df['sub_code'] = df.set_index('grade')['sub_code'].fillna(mapper)
Output: Output:
sub_code stud_level grade
0 CSE01 101 STA
1 CSE01 101 STA
2 CSE03 101 PSA
3 CSE02 101 STA
4 CSE03 101 STA
5 CSE02 101 SSA
6 CSE03 101 PSA
7 CSE02 101 QSA
df['sub_code'] =df.groupby(['grade'])['sub_code'].bfill().ffill()
sub_code stud_level grade
0 CSE01 101 STA
1 CSE01 101 STA
2 CSE03 101 PSA
3 CSE02 101 STA
4 CSE03 101 STA
5 CSE02 101 SSA
6 CSE03 101 PSA
7 CSE02 101 QSA
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