Examples with Accumulator org.apache.jena.sparql.expr.aggregate.Accumulator used on opensource projects

Example 1 with Accumulator

use of org.apache.jena.sparql.expr.aggregate.Accumulator in project jena by apache.

the class QueryIterGroup method calc.

private static Iterator<Binding> calc(final QueryIterator iter, final VarExprList groupVarExpr, final List<ExprAggregator> aggregators, final ExecutionContext execCxt) {
    return new IteratorDelayedInitialization<Binding>() {

        @Override
        protected Iterator<Binding> initializeIterator() {
            boolean noAggregators = (aggregators == null || aggregators.isEmpty());
            // Phase 1 : assign bindings to buckets by key and pump through the aggregators.
            Multimap<Binding, Pair<Var, Accumulator>> accumulators = HashMultimap.create();
            while (iter.hasNext()) {
                Binding b = iter.nextBinding();
                Binding key = genKey(groupVarExpr, b, execCxt);
                if (noAggregators) {
                    // Put in a dummy to remember the input.
                    accumulators.put(key, placeholder);
                    continue;
                }
                // Create if does not exist.
                if (!accumulators.containsKey(key)) {
                    for (ExprAggregator agg : aggregators) {
                        Accumulator x = agg.getAggregator().createAccumulator();
                        Var v = agg.getVar();
                        accumulators.put(key, Pair.create(v, x));
                    }
                }
                // Do the per-accumulator calculation.
                for (Pair<Var, Accumulator> pair : accumulators.get(key)) pair.getRight().accumulate(b, execCxt);
            }
            if (accumulators.isEmpty()) {
                if (noAggregators) {
                    // ==> 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);
            }
            if (noAggregators)
                // We used placeholder so there are always the key. 
                return accumulators.keySet().iterator();
            List<Binding> results = new ArrayList<>();
            for (Binding k : accumulators.keySet()) {
                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();
        }
    };
}