Method project_columns

dask/layers.py:452–481

Produce a column projection for this IO layer. Given a list of required output columns, this method returns the projected layer.

(self, columns)

        return self._columns

    def project_columns(self, columns):
        """Produce a column projection for this IO layer.
        Given a list of required output columns, this method
        returns the projected layer.
        """
        from dask.dataframe.io.utils import DataFrameIOFunction

        columns = list(columns)

        if self.columns is None or set(self.columns).issuperset(columns):
            # Apply column projection in IO function.
            # Must satisfy `DataFrameIOFunction` protocol
            if isinstance(self.io_func, DataFrameIOFunction):
                io_func = self.io_func.project_columns(columns)
            else:
                io_func = self.io_func

            layer = DataFrameIOLayer(
                (self.label or "subset") + "-" + tokenize(self.name, columns),
                columns,
                self.inputs,
                io_func,
                label=self.label,
                produces_tasks=self.produces_tasks,
                annotations=self.annotations,
            )
            return layer
        else:
            # Default behavior
            return self

    def __repr__(self):
        return f"DataFrameIOLayer<name='{self.name}', n_parts={len(self.inputs)}, columns={self.columns}>"