Extra "Aggregate_Sample" operators in algebra

[joc-proxem]

In the following code:

query = """
SELECT
    (COUNT(?t1) AS ?c1)
    (COUNT(?t2) AS ?c2)
    (?c1 / ?c2 * 100 AS ?p)
WHERE {
    ?t1 a :Sample .
    ?t2 a :Sample
}
"""

ns = { "": "http://example.org/" }
q = parser.parseQuery(query)
algebra = translateQuery(q, initNs = ns)

?c1 and ?c2 are wrapped in "Aggregate_Sample" operators, whereas they should not be : algorithm 18.2.4.1 (https://www.w3.org/TR/sparql11-query/#convertGroupAggSelectExpressions) states that

For each **unaggregated variable** V in X
    Replace V with Sample(V)

A possible fix could be as follows (in algebra.py):

• in translateAggregates:

   # collect/replace aggs in :
    #    select expr as ?var
    if q.projection:
        aggregated_vars = set(v.evar for v in q.projection if isinstance(v.expr, CompValue) and v.expr.name.startswith("Aggregate_"))
        for v in q.projection:
            if v.evar:
                v.expr = traverse(v.expr, functools.partial(_sample, v=v.evar, s=aggregated_vars))

• in _sample

# type error: Missing return statement
def _sample(e: typing.Union[CompValue, List[Expr], Expr, List[str], Variable], v: Optional[Variable] = None, s: Optional[set] = None) -> Optional[CompValue]:  # type: ignore[return]
    """
    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:
        if s is None or e not in s:
            return CompValue("Aggregate_Sample", vars=e)