// No rows to group, no aggregators.
// ==> No result rows.
return Iter.nullIterator() ;
}
BindingMap binding = BindingFactory.create() ;
for ( ExprAggregator agg : aggregators )
{
Var v = agg.getVar();
Node value = agg.getAggregator().getValueEmpty();
if ( value != null )
{
binding.add( v, value );
}
}
if ( binding == null )
// This does not happen if there are any aggregators.
return Iter.nullIterator() ;
// cast to get the static type inference to work.
return Iter.singletonIter((Binding)binding) ;
}
// Phase 2 : There was input and so there are some groups.
// For each bucket, get binding, add aggregator values to the binding.
// We used AccNull so there are always accumulators.
if ( noAggregators )
// We used placeholder so there are always the key.
return accumulators.keys().iterator() ;
List<Binding> results = new ArrayList<>() ;
for ( Binding k : accumulators.keys() )
{
Collection<Pair<Var, Accumulator>> accs = accumulators.get(k) ;
BindingMap b = BindingFactory.create(k) ;
for ( Pair<Var, Accumulator> pair : accs )
{
Var v = pair.getLeft() ;
NodeValue value = pair.getRight().getValue() ;
Node n = (value==null) ? null : value.asNode() ;
if ( v == null || n == null )
{}
else
b.add(v, n) ;
}
results.add(b) ;
}
return results.iterator() ;
}