使用哈希图比较键和值，并基于相似的键将值相加

Question

So i was wondering how and if it was possible using Hashmaps, one containing only strings and the other containing a similar string key but a float value, to compare them and then from that comparison print out the amount of similar values in the first hashmap, and then the float from the second hashmap added together when their keys/values line up. Example below that should clarify what i mean and to do this dynamically.

CODE

HashMap<String, String> hmap = new HashMap<>();
HashMap<String, Float> h2map = new HashMap<>();
hmap.put("order1", "pending");
hmap.put("order2", "cancelled");
hmap.put("order3", "pending");

h2map.put("order1", (float) 19.95);
h2map.put("order2", (float) 19.95);
h2map.put("order3", (float) 39.9);

Set <String> singles = new HashSet<>(h2map.values());

if(h2map.keySet().equals(hmap.keySet())) {
// below prints out the states and amount of the states but how can i get the float values from hmap to be added together for the similar states and printed with their respective state?
  for(String element : singles) {               
   System.out.println(element + ": " + Collections.frequency(hmap.values(), element));          
                    }
}

Current Output

pending: 2
cancelled: 1

Desired Output

pending: 2 $59.85
cancelled 1 $19.95

Answer 1

Is this what you want?

public static void main(String[] args) {
    HashMap<String, String> hmap = new HashMap<>();
    HashMap<String, Float> h2map = new HashMap<>();

    hmap.put("order1", "pending");
    hmap.put("order2", "cancelled");
    hmap.put("order3", "pending");

    h2map.put("order1", 19.95f);
    h2map.put("order2", 19.95f);
    h2map.put("order3", 39.9f);

    Map<String, DoubleSummaryStatistics> grouping = hmap
            .entrySet()
            .stream()
            .collect(Collectors.groupingBy(Map.Entry::getValue, Collectors.summarizingDouble(e -> h2map.get(e.getKey()))));

    grouping.forEach((key, value) -> System.out.println(key + ": " + value.getCount() + " " + value.getSum()));
}

Note that there is no summarizing statistics collector for BigDecimal and this code works only with Float or Double. But for money calculations better use BigDecimal. It's possible to implement the custom collector if needed )

Answer 2

I have replaced the use of Float with BigDecimal for better accuracy. Also I used two maps, one for holding the summed value and the other for count:

public static void main(String[] args) {
        HashMap<String, String> hmap = new HashMap<>();
        HashMap<String, BigDecimal> h2map = new HashMap<>();
        hmap.put("order1", "pending");
        hmap.put("order2", "cancelled");
        hmap.put("order3", "pending");

        h2map.put("order1", new BigDecimal("19.95"));
        h2map.put("order2", new BigDecimal("19.95"));
        h2map.put("order3", new BigDecimal("39.9"));

        //Map for holding sum 
        HashMap<String, BigDecimal> sum = new HashMap<>();

        for(String key : h2map.keySet()){
            if(hmap.get(key) != null){
                String value = hmap.get(key);
                if(sum.get(value) == null){
                    sum.put(value, h2map.get(key));
                }else{
                    sum.put(value, (sum.get(value).add(h2map.get(key))));
                }
            }
        }
        //Map for holding count
        HashMap<String, BigDecimal> countMap = new HashMap<>();
        for(Iterator<Map.Entry<String, BigDecimal>> itr = sum.entrySet().iterator(); itr.hasNext(); ){
            Map.Entry<String, BigDecimal> entry = itr.next();
            String key = entry.getKey();
            int count = Collections.frequency(hmap.values(), key);
            countMap.put((key + count), sum.get(key));
            itr.remove();
        }
        //For GC
        sum = null;
        countMap.forEach((k, v) -> System.out.println(k + " " + v));
    }