algebra.py 文件源码

def _sample(e, v=None):
    """
    For each unaggregated variable V in expr
    Replace V with Sample(V)
    """
    if isinstance(e, CompValue) and e.name.startswith("Aggregate_"):
        return e  # do not replace vars in aggregates
    if isinstance(e, Variable) and v != e:
        return CompValue('Aggregate_Sample', vars=e)