Python Pandas : how do I fill none empty rows with its corresponding column names?

Question

这是原始的df:

A   B   C 
32      4
    2   
2       
9       2
2   6   

我想用列名填写包含数据的单元格。输出将如下所示:

A   B   C 
A       C 
    B   
A       
A       C 
A   B   

谢谢 RJ

Answer 1

另一种方法是 np.where，而且速度也很快:

out = df.copy()
out[:] = np.where(df.notna(),df.columns,np.nan)

---

print(out)

     A    B    C
0    A  NaN    C
1  NaN    B  NaN
2    A  NaN  NaN
3    A  NaN    C
4    A    B  NaN