Streams on nested map

Question

I have the following usecase. I have a nested map with following structure:

Map<String, Map<WorkType, List<CostLineItem>>>

I have to iterate over the map and get the list of CLObject. If the single entry in the list has identifier as null. I have to generate the unique identifier per EnumType. I am not sure how to do it with streams? Following iteration logic will make clear what i want to accomplish

for(Map.Entry<String, Map<WorkType, List<CostLineItem>>> cliByWorkTypeIterator: clisByWorkType.entrySet()) {
       Map<WorkType, List<CostLineItem>> entryValue = cliByWorkTypeIterator.getValue();
       for(Map.Entry<WorkType, List<CostLineItem>>cliListIterator : entryValue.entrySet()) {
           List<CostLineItem> clis = cliListIterator.getValue();
           //if any CLI settlementNumber is zero this means we are in standard upload
           //TODO: Should we use documentType here? Revisit this check while doing dispute file upload
           if(clis.get(0).getSettlementNumber() == null) {
               clis.forEach(f -> f.toBuilder().settlementNumber(UUID.randomUUID().toString()).build());
           }
       }
   }

Nested loop makes the code bit boiler plate and dirty. Can someone help me with streams here?

Streams won't really help since the problem is having the nested map in the first place. A map of maps of lists is a definite code smell, and no amount of streams will make that go away. — Kayaman, Aug 02 '18 at 10:43
CostLineItem is grouped on the basis of workType and string (some identifier). If the CostLineItem.settlementNumber is null , i have to assign the settlementNumber to it. Please have a look at nested for loops. Apologies.. i know its very clumsy. I would request to see if we can simplify the loops to achieve the similar results. — user3681970, Aug 02 '18 at 10:47
You code becomes much simpler when you stop iterating over the `entrySet()` when you are just interested in the `values()`: `for( Map> map: clisByWorkType.values()) { for(List clis: map.values()) { your-if-statement } }`… — Holger, Aug 02 '18 at 10:47

Eran · Answer 1 · 2018-08-02T11:04:05.877

2

You can use flatMap to iterate over all the List<CostLineItem> values of all the inner Maps.

clisByWorkType.values() // returns Collection<Map<WorkType, List<CostLineItem>>>
              .stream() // returns Stream<Map<WorkType, List<CostLineItem>>>
              .flatMap(v->v.values().stream()) // returns Stream<List<CostLineItem>>
              .filter(clis -> clis.get(0).getSettlementNumber() == null) // filters that Stream
              .forEach(clis -> {do whatever logic you need to perform on the List<CostLineItem>});

edited Aug 02 '18 at 11:04

answered Aug 02 '18 at 10:46

Eran

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Thanks. Can you please provide comments so that i can better understand it – user3681970 Aug 02 '18 at 11:01
@user3681970 sure. – Eran Aug 02 '18 at 11:05

Ousmane D. · Answer 2 · 2018-08-02T10:55:43.247

0

clisByWorkType.values()
              .stream()
              .flatMap(e -> e.values().stream())
              .filter(clis -> clis.get(0).getSettlementNumber() == null)
              .flatMap(Collection::stream)
              .forEach(f -> f.toBuilder().settlementNumber(UUID.randomUUID().toString()).build());

edited Aug 02 '18 at 10:55

answered Aug 02 '18 at 10:49

Ousmane D.

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@Eugene yeah just got caught up in replicating the exact code from the post. – Ousmane D. Aug 02 '18 at 11:10

score 0 · Answer 3 · answered Aug 02 '18 at 10:50

0

The following is equivalent to your for-loop:

clisByWorkType.entrySet()
    .map(Map.Entry::getValue) // cliByWorkTypeIterator.getValue();
    .flatMap(m -> m.entrySet().stream())
    .map(Map.Entry::getValue)
    .map(CostLineItem::getValue)
    .filter(clis.get(0).getSettlementNumber() == null) //filter before flattening
    .flatMap(List::stream)
    .forEach(f -> f.toBuilder().settlementNumber(UUID.randomUUID().toString()).build());

answered Aug 02 '18 at 10:50

ernest_k

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I must say you "guys" are awesome. Can you please explain bit more on like what CostLineItem::getValue is doing? I am afraid. I generally do not make the code change which i dont understand completely – user3681970 Aug 02 '18 at 10:54

Streams on nested map

3 Answers3