Pandas: Data Manipulation - merge() function
merge() function
The merge() function is used to merge DataFrame or named Series objects with a database-style join.
The join is done on columns or indexes. If joining columns on columns, the DataFrame indexes will be ignored. Otherwise if joining indexes on indexes or indexes on a column or columns, the index will be passed on.
Syntax:
pandas.merge(left, right, how='inner', on=None, left_on=None, right_on=None, left_index=False, right_index=False, sort=False, suffixes=('_x', '_y'), copy=True, indicator=False, validate=None)
Parameters:
Name | Description | Type | Default | Required / Optional |
---|---|---|---|---|
left | The given DataFrame. | DataFrame | Required | |
right | The given DataFrame or named Series.. | DataFrame or named Series | Required | |
how | Type of merge to be performed.
|
{‘left’, ‘right’, ‘outer’, ‘inner’} | Default: ‘inner’ | Required |
on | Column or index level names to join on. These must be found in both DataFrames. If on is None and not merging on indexes then this defaults to the intersection of the columns in both DataFrames. |
label or list | Optional | |
left_on | Column or index level names to join on. These must be found in both DataFrames. If on is None and not merging on indexes then this defaults to the intersection of the columns in both DataFrames. |
label or list, or array-like | Optional | |
right_on | Column or index level names to join on in the right DataFrame. Can also be an array or list of arrays of the length of the right DataFrame. These arrays are treated as if they are columns. | label or list, or array-like | Optional | |
left_index | Use the index from the left DataFrame as the join key(s). If it is a MultiIndex, the number of keys in the other DataFrame (either the index or a number of columns) must match the number of levels. |
bool | Default: False | Optional |
right_index | Use the index from the right DataFrame as the join key. Same caveats as left_index. | bool | Default: False | Optional |
sort | Sort the join keys lexicographically in the result DataFrame. If False, the order of the join keys depends on the join type (how keyword). | bool | Default: False | Optional |
suffixes | Suffix to apply to overlapping column names in the left and right side, respectively. To raise an exception on overlapping columns use (False, False). | tuple of (str, str) | Default: (‘_x’, ‘_y’) | Optional |
copy | If False, avoid copy if possible. | bool | Default: True | Optional |
indicator | If True, adds a column to output DataFrame called "_merge" with information on the source of each row. If string, column with information on source of each row will be added to output DataFrame, and column will be named value of string. |
bool or str | Default: False | Optional |
validate | If specified, checks if merge is of specified type.
|
str | Optional |
Returns: A DataFrame of the two merged objects.
Example:
Download the Pandas DataFrame Notebooks from here.
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