Using Merge On A Column And Index In Pandas

I have two separate dataframes that share a project number. In type_df, the project number is the index. In time_df, the project number is a column. I would like to count the numbe

Solution 1:

If you want to use an index in your merge you have to specify left_index=True or right_index=True, and then use left_on or right_on. For you it should look something like this:

merged = pd.merge(type_df, time_df, left_index=True, right_on='Project')

Solution 2:

Another solution is use DataFrame.join:

df3 = type_df.join(time_df, on='Project')

For version pandas 0.23.0+the on, left_on, and right_on parameters may now refer to either column names or index level names:

left_index = pd.Index(['K0', 'K0', 'K1', 'K2'], name='key1')
left = pd.DataFrame({'A': ['A0', 'A1', 'A2', 'A3'],
                    'B': ['B0', 'B1', 'B2', 'B3'],
                     'key2': ['K0', 'K1', 'K0', 'K1']},
                    index=left_index)
                    
right_index = pd.Index(['K0', 'K1', 'K2', 'K2'], name='key1')

right = pd.DataFrame({'C': ['C0', 'C1', 'C2', 'C3'],
                     'D': ['D0', 'D1', 'D2', 'D3'],
                     'key2': ['K0', 'K0', 'K0', 'K1']},
                      index=right_index)
          
print (left)    
       A   B key2
key1             
K0    A0  B0   K0
K0    A1  B1   K1
K1    A2  B2   K0
K2    A3  B3   K1
        
print (right)
       C   D key2
key1             
K0    C0  D0   K0
K1    C1  D1   K0
K2    C2  D2   K0
K2    C3  D3   K1

---

df = left.merge(right, on=['key1', 'key2'])
print (df)
       A   B key2   C   D
key1                     
K0    A0  B0   K0  C0  D0
K1    A2  B2   K0  C1  D1
K2    A3  B3   K1  C3  D3

Solution 3:

You must have the same column in each dataframe to merge on.

In this case, just make a 'Project' column for type_df, then merge on that:

type_df['Project'] = type_df.index.values
merged = pd.merge(time_df,type_df, on='Project', how='inner')
merged
#    Project  Time Project Type#0  Project1    13       Type 2#1  Project1    12       Type 2#2  Project2    41       Type 1print merged[merged['Project Type'] == 'Type 2']['Project Type'].count()
2