Merge and Join Operations

Combining DataFrames

Pandas provides multiple ways to combine DataFrames.

Merge

pd.merge(df1, df2, on='key') performs inner merge on key. Types: 'inner', 'outer', 'left', 'right'.

Multiple keys: on=['key1', 'key2']. Suffixes for overlapping columns: suffixes=('_left', '_right').

Join

df1.join(df2) joins on index. df1.join(df2, how='outer') for outer join.

set_index before joining to use index as key.

Concatenation

pd.concat([df1, df2]) stacks rows. axis=1 for columns. ignore_index resets index.

Key Takeaways

1. Merge combines DataFrames on columns
2. Join combines on index
3. Concatenation stacks DataFrames