Transform with group by in Pandas

I am creating a Dataframe

import pandas as pd

 df1 = pd.DataFrame( {     
"Name" : ["Alice", "Bob", "Mallory", "Mallory", "Bob" , "Mallory"] ,           
"City" : ["Seattle", "Seattle", "Portland", "Seattle", "Seattle",     
"Portland"]   } )          

df1.groupby( ["City"] )['Name'].transform(lambda x:     
','.join(x)).drop_duplicates()      
I want the output as      

Name    City                 
Alice,Bob,Mallory,Bob     Seattle           
Mallory,Mallory    Portland        

but i am getting only           
Name         
Alice,Bob,Mallory,Bob                
Mallory,Mallory        

This is an example with small number of columns but in my actual problem i 
have too many columns so i cannot use           
df1['Name']= df1.groupby( ['City'] )['Name'].transform(lambda x:         
','.join(x))              
df1.groupby( ['City','Name'], as_index=False )              
df1.drop_duplicates()          

because for each column i have to write the same code
Is there any way to do it without writing transform for each column individually.