merge how pandas code example

Example 1: pandas left join

df.merge(df2, left_on = "doc_id", right_on = "doc_num", how = "left")

Example 2: joins in pandas

pd.merge(product,customer,left_on='Product_name',right_on='Purchased_Product')

Example 3: pandas merge python

import pandas as pd
df1 = pd.DataFrame({'lkey': ['foo', 'bar', 'baz', 'foo'],
                    'value': [1, 2, 3, 5]})
df2 = pd.DataFrame({'rkey': ['foo', 'bar', 'baz', 'foo'],
                    'value': [5, 6, 7, 8]})
df1.merge(df2, left_on='lkey', right_on='rkey')

Example 4: merge dataframe in python

In [1]: df1 = pd.DataFrame({'A': ['A0', 'A1', 'A2', 'A3'],
   ...:                     'B': ['B0', 'B1', 'B2', 'B3'],
   ...:                     'C': ['C0', 'C1', 'C2', 'C3'],
   ...:                     'D': ['D0', 'D1', 'D2', 'D3']},
   ...:                    index=[0, 1, 2, 3])
   ...: 

In [2]: df2 = pd.DataFrame({'A': ['A4', 'A5', 'A6', 'A7'],
   ...:                     'B': ['B4', 'B5', 'B6', 'B7'],
   ...:                     'C': ['C4', 'C5', 'C6', 'C7'],
   ...:                     'D': ['D4', 'D5', 'D6', 'D7']},
   ...:                    index=[4, 5, 6, 7])
   ...: 

In [3]: df3 = pd.DataFrame({'A': ['A8', 'A9', 'A10', 'A11'],
   ...:                     'B': ['B8', 'B9', 'B10', 'B11'],
   ...:                     'C': ['C8', 'C9', 'C10', 'C11'],
   ...:                     'D': ['D8', 'D9', 'D10', 'D11']},
   ...:                    index=[8, 9, 10, 11])
   ...: 

In [4]: frames = [df1, df2, df3]

In [5]: result = pd.concat(frames)

Example 5: python merge using or statement

dupes = (df.B_on_A_match_1 == df.B_on_A_match_2) # also could remove A_on_B_match
df.loc[~dupes]

     A  A_on_B_match_1  A_on_B_match_2    B  B_on_A_match_1  B_on_A_match_2
0  1.0             NaN             NaN  NaN             9.0             4.0
0  NaN             2.0             6.0  8.0             NaN             NaN
1  NaN             4.0             4.0  5.0             NaN             NaN

Example 6: take union of two dataframes pandas

m = {'left_only': 'df1', 'right_only': 'df2', 'both': 'df1, df2'}

result = df1.merge(df2, on=['A'], how='outer', indicator='B')
result['B'] = result['B'].map(m)

result