pandas combine two columns with null values

Question

I have a df with two columns and I want to combine both columns ignoring the NaN values. The catch is that sometimes both columns have NaN values in which case I want the new co

Answer 1

1. You can replace the non zero values with column names like

   df1= df.replace(1, pd.Series(df.columns, df.columns))

2. Replace 0's with empty string and then merge the columns like below

   f = f.replace(0, '') f['new'] = f.First+f.Second+f.Three+f.Four

Refer the full code below.

import pandas as pd
df = pd.DataFrame({'Second':[0,1,0,0],'First':[1,0,0,0],'Three':[0,0,1,0],'Four':[0,0,0,1], 'cl': ['3D', 'Wireless','Accounting','cisco']})
df2=pd.DataFrame({'pi':['Accounting','cisco','3D','Wireless']})
df1= df.replace(1, pd.Series(df.columns, df.columns))
f = pd.merge(df1,df2,how='right',left_on=['cl'],right_on=['pi'])
f = f.replace(0, '')
f['new'] = f.First+f.Second+f.Three+f.Four

df1:

In [3]: df1                                                                                                                                                                              
Out[3]: 
   Second  First  Three  Four          cl
0       0  First      0     0          3D
1  Second      0      0     0    Wireless
2       0      0  Three     0  Accounting
3       0      0      0  Four       cisco

df2:

In [4]: df2                                                                                                                                                                              
Out[4]: 
           pi
0  Accounting
1       cisco
2          3D
3    Wireless

Final df will be:

In [2]: f                                                                                                                                                                                
Out[2]: 
   Second  First  Three  Four          cl          pi     new
0          First                       3D          3D   First
1  Second                        Wireless    Wireless  Second
2                 Three        Accounting  Accounting   Three
3                        Four       cisco       cisco    Four