Method query

dask/dataframe/dask_expr/_collection.py:3609–3667

Filter dataframe with complex expression Blocked version of pd.DataFrame.query Parameters ---------- expr: str The query string to evaluate. You can refer to column names that are not valid Python variable names by surrounding the

(self, expr, **kwargs)

        )

    def query(self, expr, **kwargs):
        """Filter dataframe with complex expression

        Blocked version of pd.DataFrame.query

        Parameters
        ----------
        expr: str
            The query string to evaluate.
            You can refer to column names that are not valid Python variable names
            by surrounding them in backticks.
            Dask does not fully support referring to variables using the '@' character,
            use f-strings or the ``local_dict`` keyword argument instead.

        See also
        --------
        pandas.DataFrame.query
        pandas.eval

        Examples
        --------
        >>> import pandas as pd
        >>> import dask.dataframe as dd
        >>> df = pd.DataFrame({'x': [1, 2, 1, 2],
        ...                    'y': [1, 2, 3, 4],
        ...                    'z z': [4, 3, 2, 1]})
        >>> ddf = dd.from_pandas(df, npartitions=2)

        Refer to column names directly:

        >>> ddf.query('y > x').compute()
           x  y  z z
        2  1  3    2
        3  2  4    1

        Refer to column name using backticks:

        >>> ddf.query('`z z` > x').compute()
           x  y  z z
        0  1  1    4
        1  2  2    3
        2  1  3    2

        Refer to variable name using f-strings:

        >>> value = 1
        >>> ddf.query(f'x == {value}').compute()
           x  y  z z
        0  1  1    4
        2  1  3    2

        Refer to variable name using ``local_dict``:

        >>> ddf.query('x == @value', local_dict={"value": value}).compute()
           x  y  z z
        0  1  1    4
        2  1  3    2
        """