Excel Lambda functions for Power Query Table functions

EXTAB

/* USE NAMESPACE "Table" */

Item = LAMBDA(_table, _index,
    MAKEARRAY(
        2,
        COLUMNS(_table),
        LAMBDA(ir, ic, CHOOSE(ir, INDEX(_table, 1, ic), INDEX(_table, _index + 1, ic)))
    )
);

SelectRows = LAMBDA(_table, _condition, 
    LET(
        selected, MAKEARRAY(
            ROWS(_table),
            1,
            LAMBDA(ir, ic, _condition(Table.Item(_table, ir)))
        ),
        FILTER(_table, selected)
    )
);

AddKey = LAMBDA(_table, _columnname,
    LET(
        ct, ROWS(_table),
        MAKEARRAY(
            ct,
            COLUMNS(_table) + 1,
            LAMBDA(ir, ic,
                IF(
                    ic = 1,
                    IF(ir = 1, _columnname, ir - 1),
                    INDEX(_table, ir, ic - 1)
                )
            )
        )
    )
);

Column = LAMBDA(_table, _columnname,
    LET(
        columnnames, Table.ColumnNames(_table),
        colpos, List.PositionOf(columnnames, _columnname),
        INDEX(_table, 0, colpos)
    )
);

ColumnNames = LAMBDA(_table, TRANSPOSE(INDEX(_table, 1, 0)));

SelectColumns = LAMBDA(_table, _columns,
    LET(
        columnnames, Table.ColumnNames(_table),
        MAKEARRAY(
            ROWS(_table),
            COUNTA(ISERROR(_columns)),
            LAMBDA(ir, ic,
                LET(
                    colname, INDEX(_columns, ic),
                    colpos, List.PositionOf(columnnames, colname),
                    IF(
                        ir = 1,
                        colname,
                        INDEX(_table, ir, colpos)
                    )
                )
            )
        )
    )
);