'Resolve the grouping axes field selectors
@param rows: the rows field selector
@param cols: the columns field selector'

def resolve_axes(self, rows, cols):

    resource = self.resource
    rfields = self.rfields
    rows_rfield = None
    if rows:
        try:
            rows_rfield = resource.resolve_selector(rows)
        except (AttributeError, SyntaxError):
            rows_rfield = None
    cols_rfield = None
    if cols:
        try:
            cols_rfield = resource.resolve_selector(cols)
        except (AttributeError, SyntaxError):
            cols_rfield = None
    rfields['rows'] = rows_rfield
    rfields['cols'] = cols_rfield
