def row_val_lt(M, col_name, boundary):
    """Picks rows for which cell is less than to a specified value

    To be used as a 'func' argument in choose_rows_where, remove_rows_where, 
    or where_all_are_true (see module documentation).

    Parameters
    ----------
    M : numpy.ndarray
        structured array
    col_name : str
        name of column to check
    boundary : number
        value which cell must be less than

    Returns
    -------
    numpy.ndarray
        boolean array: True if row picked, False if not.

    """
    return M[col_name] < boundary