def __init__(self, expr, filter=None, skip_na=True):
FilteredExpression.__init__(self, expr, filter)
self.skip_na = skip_na
def __init__(self, varname, regime, expr=None, filter=None, yearleg=None):
FilteredExpression.__init__(self, expr, filter)
self.varname = varname
self.regime = regime
self.yearleg = yearleg
