按索引将 arrays 中的元素分组到列表中<map<string,object> &gt; </map<string,object>

Question

I have a Map<String, Object[]> in which key is the Array's name Object identifier aka collection name and its corresponding array of Objects.

The objective is to be able to Merge the different entries of the Object [] into a List<Map<String,Object>> where the keys of each Map corresponds to the known Collection name and the Object is the iTh value of each array.

In order to clarify this more:

Lets say we have a Map<String, Object[]> with the following arrays.

    Map<String, Object[]> map = new HasMap<>();

    Object[] ints = Stream.of(1,2,3,4,5).toArray();
    Object[] dobules = Stream.of(1.0,2.0,3.0,4.0,5.0).toArray();
    Object[] strings = Stream.of("a","b","c","d","e").toArray();

    map.put("ints", ints);
    map.put("doubles", dobules);
    map.put("strings", strings);

Then the output of this entry should be like this:

List<Map<String,Object>> where for the example up the List of maps would be like this

{"ints": 1, "doubles":1.0, "strings":"a"},
{"ints": 2, "doubles":2.0, "strings":"b"},
{"ints": 3, "doubles":3.0, "strings":"c"},
{"ints": 4, "doubles":4.0, "strings":"d"},
{"ints": 5, "doubles":5.0, "strings":"e"}

I am looking specially a solution using java Collection streams Thank you so much

Answer 1

Plain old approach:

List<Map<String, Object>> result = new ArrayList<>();

if(!map.isEmpty()) 
    // Assume all the array lengths are the same
    int length = map.values().iterator().next().length;

    for(int i = 0; i < length; i++) {
        Map<String, Object> row = new HashMap<>();
        for(Map.Entry<String, Object[]> entry : map.entrySet()) {
           row.put(entry.getKey(), entry.getValue()[i]; 
        }
        result.add(row);
    }
}

---

Mixed approach:

int length = map.values().iterator().next().length;

for(int i = 0; i < length; i++) {
    final int index = i; // make compiler happy
    result.add(map.entrySet()
                  .stream()
                  .collect(toMap(Map.Entry::getKey, e -> e.getValue()[index])));
}

---

Pure functional approach:

int length = map.isEmpty() ? 0 : map.values().iterator().next().length;

List<Map<String, Object>> result = 
    IntStream.range(0, length)
             .boxed()
             .map(i -> map.entrySet()
                          .stream()
                          .collect(toMap(Map.Entry::getKey, e -> e.getValue()[i])))
             .collect(toList());