def METHOD_NAME(self):
    """
    Updates the complete list of active variables for x/y axis labels.
    """
    n = len(self._groups)
    x_vars = [[]]*n
    y_vars = [[]]*n
    y2_vars = [[]]*n
    for i in range(n):
        group = self._groups[i]
        if group.isValid():
            x, y, y2 = group.getAxisLabels()
            x_vars[i] = [x]
            y_vars[i] = y
            y2_vars[i] = y2
    self.variablesChanged.emit(x_vars, y_vars, y2_vars)