Excel Lambda functions for Power Query Table functions

EX_Table

/* USE NAMESPACE "Table" */

Item = LAMBDA(_table, _index,
    LET(
        // Help
        Help, TRIM(TEXTSPLIT(
            "DESCRIPTION:->Returns the row at position _index from _table including the header row\nVERSION:->1.0\nPARAMETERS:->_table as table, _index as number",
            "->",
            "\n"
        )),
        // Error Messages
        ErrorMessages, {"_index is not a number."},
        // Check Inputs: 1 if _index is not a number, otherwise 0
        CheckInputs, IF(NOT(ISNUMBER(_index)), 1, 0),
        // Procedure
        Result, MAKEARRAY(
            2,
            COLUMNS(_table),
            LAMBDA(ir, ic, CHOOSE(ir, INDEX(_table, 1, ic), INDEX(_table, _index + 1, ic)))
        ),
        // Return Result or Help/Error
        CHOOSE(CheckInputs + 1,
            Result,
            Help,
            INDEX(ErrorMessages, CheckInputs)
        )
    )
);

SelectRows = LAMBDA(_table, _condition,
    LET(
        // Help
        Help, TRIM(TEXTSPLIT(
            "DESCRIPTION:->Filters _table rows where _condition returns TRUE for that row.\nVERSION:->1.0\nPARAMETERS:->_table as table, _condition as function",
            "->",
            "\n"
        )),
        // No error messages since types cannot easily be checked
        ErrorMessages, {},
        CheckInputs, 0,
        // Procedure
        selected, MAKEARRAY(
            ROWS(_table),
            1,
            LAMBDA(ir, ic, _condition(Table.Item(_table, ir)))
        ),
        Result, FILTER(_table, selected),
        CHOOSE(CheckInputs + 1,
            Result,
            Help,
            ""
        )
    )
);

AddKey = LAMBDA(_table, _columnname,
    LET(
        // Help
        Help, TRIM(TEXTSPLIT(
            "DESCRIPTION:->Adds an index column named _columnname to _table.\nVERSION:->1.0\nPARAMETERS:->_table as table, _columnname as text",
            "->",
            "\n"
        )),
        ErrorMessages, {"_columnname is not text."},
        CheckInputs, IF(NOT(ISTEXT(_columnname)), 1, 0),
        ct, ROWS(_table),
        Result, MAKEARRAY(
            ct,
            COLUMNS(_table) + 1,
            LAMBDA(ir, ic,
                IF(
                    ic = 1,
                    IF(ir = 1, _columnname, ir - 1),
                    INDEX(_table, ir, ic - 1)
                )
            )
        ),
        CHOOSE(CheckInputs + 1,
            Result,
            Help,
            INDEX(ErrorMessages, CheckInputs)
        )
    )
);

Column = LAMBDA(_table, _columnname,
    LET(
        Help, TRIM(TEXTSPLIT(
            "DESCRIPTION:->Returns a column from _table with the name _columnname.\nVERSION:->1.0\nPARAMETERS:->_table as table, _columnname as text",
            "->",
            "\n"
        )),
        ErrorMessages, {"_columnname is not text."},
        CheckInputs, IF(NOT(ISTEXT(_columnname)), 1, 0),
        columnnames, Table.ColumnNames(_table),
        colpos, List.PositionOf(columnnames, _columnname),
        Result, INDEX(_table, 0, colpos),
        CHOOSE(CheckInputs + 1,
            Result,
            Help,
            INDEX(ErrorMessages, CheckInputs)
        )
    )
);

ColumnNames = LAMBDA(_table,
    LET(
        Help, TRIM(TEXTSPLIT(
            "DESCRIPTION:->Returns a list of column names from _table.\nVERSION:->1.0\nPARAMETERS:->_table as table",
            "->",
            "\n"
        )),
        // no error checks
        Result, TRANSPOSE(INDEX(_table, 1, 0)),
        // Always return result by default; help when invoked accordingly
        CHOOSE(1, Result, Help, "")
    )
);

SelectColumns = LAMBDA(_table, _columns,
    LET(
        Help, TRIM(TEXTSPLIT(
            "DESCRIPTION:->Returns a new table containing only the columns listed in _columns.\nVERSION:->1.0\nPARAMETERS:->_table as table, _columns as list",
            "->",
            "\n"
        )),
        ErrorMessages, {},
        CheckInputs, 0,
        columnnames, Table.ColumnNames(_table),
        Result, LET(
            cnt, COUNTA(_columns),
            MAKEARRAY(
                ROWS(_table),
                cnt,
                LAMBDA(ir, ic,
                    LET(
                        colname, INDEX(_columns, ic),
                        colpos, List.PositionOf(columnnames, colname),
                        IF(
                            ir = 1,
                            colname,
                            INDEX(_table, ir, colpos)
                        )
                    )
                )
            )
        ),
        CHOOSE(CheckInputs + 1,
            Result,
            Help,
            ""
        )
    )
);