private void modifyFieldValue(String name, String fieldName, double delta) {
		FieldValueCounter counter = getOrCreate(name);
		Map<String, Double> data = counter.getFieldValueCount();
		double count = data.containsKey(fieldName) ? data.get(fieldName) : 0;
		data.put(fieldName, count + delta);
		save(counter);
	}
Memory backed implementation of FieldValueCounterRepository that uses a ConcurrentMap

@author Mark Pollack
spring-xd-analytics/src/main/java/org/springframework/xd/analytics/metrics/memory/InMemoryFieldValueCounterRepository.java