如何在java lambda中将String[]转换为以数组索引作为求和值的映射？

Question

我有以下内容

new ConstructStateMachine(new String[] {
      "a", "b", "c", "aa", "d", "b"
}, 1, 5);

并且我想将这个数组转换为map 。

indices | 0 | 1 | 2 | 3  | 4 | 5 |
item    | a | b | c | aa | d | b |
value   | 1 | 2 | 3 | 4  | 5 | 6 |

// pseudo-code
Map<String, Integer> dictionary = new HashMap<>(
   ("b"  => 8) // because "b" appeared in index 1 and 5
   ("c"  => 3)
   ("aa" => 4)
   ("d"  => 5)
);

Map < String, List < Integer >> table = new HashMap < > ();


// I thought of doing an intersection of two arrays and get the value from there
// but that just made things more complicated
String[] a = (Arrays.stream(dictionary)
  .filter(x - > Arrays.stream(newDis)
    .anyMatch(y - > Objects.equals(y, x))
  )
).toArray(String[]::new);


// in here, I tried looping and created the value that starts from 1 to 6, rather than
// from 0 to 5
IntStream.range(0, this.newDis.length).forEach(idx - > {
  List<Integer> currentValue = table.computeIfAbsent(newDis[idx], k - > new ArrayList<>());
  currentValue.add(idx + 1);
});

但我无法将字符串数组转换为map

Answer 1

String[] array = new String[] {"a", "b", "c", "aa", "d", "b"};
Map<String, Integer> result =
    IntStream.range(0, array.length)
             .boxed()
             .collect(Collectors.toMap(i -> array[i], i -> i + 1, Integer::sum));

或者，使用一个简单的循环，使代码更可重复和直观，imo:

Map<String, Integer> result = new HashMap<>();
for (int i = 0; i < array.length; i++) {
    result.merge(array[i], i + 1, Integer::sum);
}