} else if(op instanceof MultipleParallelDo) {
MultipleParallelDo mPDo = (MultipleParallelDo) op;
parent = execute((LazyCollection)mPDo.getOrigin());
DoFn function = (DoFn)mPDo.getDests().get(output); // get the function that corresponds to this collection
for (Object obj : parent) {
function.process(obj, emitter);
}
// GroupByKey
} else if(op instanceof GroupByKey) {
GroupByKey gBK = (GroupByKey) op;
parent = execute(gBK.getOrigin());