Repository: pandas-dev/pandas
File: pandas/core/reshape/merge.py (Python)

Code before:
    Sorting by any additional 'by' grouping columns is not required.

    For each row in the left DataFrame:

      - A "backward" search selects the last row in the right DataFrame whose
        'on' key is less than or equal to the left's key.

      - A "forward" search selects the first row in the right DataFrame whose
        'on' key is greater than or equal to the left's key.

      - A "nearest" search selects the row in the right DataFrame whose 'on'
        key is closest in absolute distance to the left's key.

    Optionally match on equivalent keys with 'by' before searching with 'on'.

    Parameters
    ----------
    left : DataFrame or named Series
        First pandas object to merge.
    right : DataFrame or named Series
        Second pandas object to merge.
    on : label
        Field name to join on. Must be found in both DataFrames.
        The data MUST be in ascending order. Furthermore this must be
        a numeric column, such as datetimelike, integer, or float. 'on'
        or 'left_on' / 'right_on' must be given.
    left_on : label
        Field name to join on in left DataFrame. If specified, sort the left
        DataFrame by this column in ascending order before merging.
    right_on : label
        Field name to join on in right DataFrame. If specified, sort the right
        DataFrame by this column in ascending order before merging.
    left_index : bool
        Use the index of the left DataFrame as the join key.
    right_index : bool
        Use the index of the right DataFrame as the join key.
    by : column name or list of column names
        Match on these columns before performing merge operation. It is not required
        to sort by these columns.
    left_by : column name
        Field names to match on in the left DataFrame.
    right_by : column name
        Field names to match on in the right DataFrame.
    suffixes : 2-length sequence (tuple, list, ...)
        Suffix to apply to overlapping column names in the left and right
        side, respectively.
    tolerance : int or timedelta, optional, default None
        Select asof tolerance within this range; must be compatible
        with the merge index.
    allow_exact_matches : bool, default True


Review comment (suggestion):
```suggestion
        a numeric column, such as datetimelike, integer, or float. ``on``
        or ``left_on`` / ``right_on`` must be given.
```

Code after:
    Sorting by any additional 'by' grouping columns is not required.

    For each row in the left DataFrame:

      - A "backward" search selects the last row in the right DataFrame whose
        'on' key is less than or equal to the left's key.

      - A "forward" search selects the first row in the right DataFrame whose
        'on' key is greater than or equal to the left's key.

      - A "nearest" search selects the row in the right DataFrame whose 'on'
        key is closest in absolute distance to the left's key.

    Optionally match on equivalent keys with 'by' before searching with 'on'.

    Parameters
    ----------
    left : DataFrame or named Series
        First pandas object to merge.
    right : DataFrame or named Series
        Second pandas object to merge.
    on : label
        Field name to join on. Must be found in both DataFrames.
        The data MUST be in ascending order. Furthermore this must be
        a numeric column, such as datetimelike, integer, or float. ``on``
        or ``left_on`` / ``right_on`` must be given.
    left_on : label
        Field name to join on in left DataFrame. If specified, sort the left
        DataFrame by this column in ascending order before merging.
    right_on : label
        Field name to join on in right DataFrame. If specified, sort the right
        DataFrame by this column in ascending order before merging.
    left_index : bool
        Use the index of the left DataFrame as the join key.
    right_index : bool
        Use the index of the right DataFrame as the join key.
    by : column name or list of column names
        Match on these columns before performing merge operation. It is not required
        to sort by these columns.
    left_by : column name
        Field names to match on in the left DataFrame.
    right_by : column name
        Field names to match on in the right DataFrame.
    suffixes : 2-length sequence (tuple, list, ...)
        Suffix to apply to overlapping column names in the left and right
        side, respectively.
    tolerance : int or timedelta, optional, default None
        Select asof tolerance within this range; must be compatible
        with the merge index.
    allow_exact_matches : bool, default True