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

Question

Here's the original df:

A   B   C 
32      4
    2   
2       
9       2
2   6   

I want to fill in cells that have data with the column names.The output will look like this:

A   B   C 
A       C 
    B   
A       
A       C 
A   B   

Thanks RJ

Answer 1

Another way is np.where and would be very fast as well:

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

Answer 2

We could do stack and unstack

s=df.stack()
s[:]=s.index.get_level_values(1)
s=s.unstack()
s
Out[496]: 
     A    B    C
0    A  NaN    C
1  NaN    B  NaN
2    A  NaN  NaN
3    A  NaN    C
4    A    B  NaN