Method ix_ref

python/pathway/internals/table.py:2662–2749

Reindexes the table using expressions as primary keys. Uses keys from context, or tries to infer proper context from the expression. If ``optional`` is True, then None in expression values result in None values in the result columns. Missing values in table keys result in Run

(
        self,
        *args: expr.ColumnExpression | Value,
        optional: bool = False,
        context=None,
        instance: expr.ColumnReference | None = None,
        allow_misses: bool = False,
    )

    @trace_user_frame
    def ix_ref(
        self,
        *args: expr.ColumnExpression | Value,
        optional: bool = False,
        context=None,
        instance: expr.ColumnReference | None = None,
        allow_misses: bool = False,
    ):
        """Reindexes the table using expressions as primary keys.
        Uses keys from context, or tries to infer proper context from the expression.
        If ``optional`` is True, then None in expression values result in None values in the result columns.
        Missing values in table keys result in RuntimeError.
        If ``allow_misses`` is set to True, they result in None value on the output.

        Context can be anything that allows for `select` or `reduce`, or `pathway.this` construct
        (latter results in returning a delayed operation, and should be only used when using `ix` inside
        join().select() or groupby().reduce() sequence).


        Args:
            args: Column references.

        Returns:
            Row: indexed row.

        Example:

        >>> import pathway as pw
        >>> t1 = pw.debug.table_from_markdown('''
        ... name   | pet
        ... Alice  | dog
        ... Bob    | cat
        ... Carole | cat
        ... David  | dog
        ... ''')
        >>> t2 = t1.with_id_from(pw.this.name)
        >>> t2 = t2.select(*pw.this, new_value=pw.this.ix_ref("Alice").pet)
        >>> pw.debug.compute_and_print(t2, include_id=False)
        name   | pet | new_value
        Alice  | dog | dog
        Bob    | cat | dog
        Carole | cat | dog
        David  | dog | dog

        Tables obtained by a groupby/reduce scheme always have primary keys:

        >>> import pathway as pw
        >>> t1 = pw.debug.table_from_markdown('''
        ... name   | pet
        ... Alice  | dog
        ... Bob    | cat
        ... Carole | cat
        ... David  | cat
        ... ''')
        >>> t2 = t1.groupby(pw.this.pet).reduce(pw.this.pet, count=pw.reducers.count())
        >>> t3 = t1.select(*pw.this, new_value=t2.ix_ref(t1.pet).count)
        >>> pw.debug.compute_and_print(t3, include_id=False)
        name   | pet | new_value