pd merge on multiple columns
new_df = pd.merge(A_df, B_df,  how='left', left_on=['A_c1','c2'], right_on = ['B_c1','c2'])
                                
                            pd merge on multiple columns
new_df = pd.merge(A_df, B_df,  how='left', left_on=['A_c1','c2'], right_on = ['B_c1','c2'])
                                
                            concat 3 column in pandas
In[17]:df['combined']=df['bar'].astype(str)+'_'+df['foo']+'_'+df['new']
In[17]:df
Out[18]: 
   bar foo     new    combined
0    1   a   apple   1_a_apple
1    2   b  banana  2_b_banana
2    3   c    pear    3_c_pear
                                
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