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How to merge Python Pandas data frames?

To merge Python Pandas data frames, we can call the merge method.

For instance, we write

left = pd.DataFrame({'key': ['A', 'B', 'C', 'D'], 'value': np.random.randn(4)})
right = pd.DataFrame({'key': ['B', 'D', 'E', 'F'], 'value': np.random.randn(4)})
m = left.merge(right, on='key')

to create the left and right dataframes with some random values.

Then we call left.merge with right and set on to 'key' to merge the rows by the key column value.

This will do an inner join.

We can also add the how argument to merge to do other kinds of joins.

So we can write

left.merge(right, on='key', how='left')

to set how to 'left' to do a left join.

We can also set how to 'right' or 'outer' to do those joins.

Posted in Python, Python Answers