List<KeyValueReader> kvReaderList = new ArrayList<KeyValueReader>(keyValueReaders);
// this sets up the map operator contexts correctly
mapOp.initializeContexts();
Deserializer deserializer = mapOp.getCurrentDeserializer();
KeyValueReader reader =
new KeyValueInputMerger(kvReaderList, deserializer,
new ObjectInspector[] { deserializer.getObjectInspector() }, mapOp
.getConf()
.getSortCols());
return reader;
}