英文:
Reducing a Collection in Java 8
问题
我想知道什么是最清晰、也许是最惯用的方式来处理类似于以下简单示例的情况。
如果我有一个数组（或列表等）[1,1,1,2,3,5,5,9]，我想要进行一种归约操作，类似于折叠，其中连续的数字会相加，只留下一个元素。
因此[1,1,1,2,3,5,5,9]会变成[3,2,3,10,9]。
稍微更一般化的情况：
[object1, object2, object3, object4]，其中object1和object2具有某些属性的组合，这将使得需要创建一个新的object5来替换它们两个，结果将变为[object5, object3, object4]。
我的实际用例要复杂一些，但基本思想是类似的，在某种程度上迭代处理列表，但不是归约为单个原子值。
英文:
I am wondering what is the cleanest , perhaps idiomatic, way to something like the following trivial example.
If I have an array (or list, etc) [1,1,1,2,3,5,5,9] I want to do a reduction, fold, of sorts, where consecutive numbers are added, leaving only one element.
So [1,1,1,2,3,5,5,9] would become [3,2,3,10,9].
A slightly more generalized case:
[object1, object2, object3, object4] where object1 and object2 have some combination of properties that would make it necessary to create a new object5 to replace both of them and the result would be [object5, object3, object4].
My actual use case is a bit more complicated, but the idea is similar in iterating over a list, somehow, but not reducing to a single atomic value.
答案1
得分: 0
减少Stream API的工作方式不是这样的。 减少（也称为fold）的重点是将输入元素合并为单个结果。
只要计算依赖于基于等价性的连续元素，这显然不适合Stream API。
你想要做类似这样的事情*...但是我不知道如何将其“转换”为Stream API。
List<Integer> list = Arrays.asList(1, 1, 1, 2, 3, 5, 5, 9);
List<Integer> newList = new ArrayList<>();
int i = 0;
while (i < list.size()) {
int current = list.get(i);
int next = current;
int sum = 0;
int j = i;
while (current == next) {
j++;
sum += next;
if (j < list.size()) {
next = list.get(j);
} else break;
}
newList.add(sum);
i = j;
}
// [3, 2, 3, 10, 9]
System.out.println(newList);
*从性能和可读性的角度来看，这显然不是最佳解决方案，只要我在解决“LeetCode”问题方面真的很差。思路是展示这些解决方案与Stream API不兼容。
英文:
The reduction is Stream API doesn't work this way. The point of the reduction (also called as fold) is to combine input elements into a single result.
This is clearly not a suitable task for Stream API as long as the computation relies on the consecutive elements based on the equivalence.
You want go for something like this*... which I have no idea to "convert" into Stream API.
List<Integer> list = Arrays.asList(1,1,1,2,3,5,5,9);
List<Integer> newList = new ArrayList<>();
int i = 0;
while (i < list.size()) {
int current = list.get(i);
int next = current;
int sum = 0;
int j = i;
while (current == next) {
j++;
sum += next;
if (j < list.size()) {
next = list.get(j);
} else break;
}
newList.add(sum);
i = j;
}
// [3, 2, 3, 10, 9]
System.out.println(newList);
*This is clearly not the best solution in terms of performance and readability as long as I really suck in "LeetCode" problems solving. The idea is to demonstrate these solutions don't go well with Stream API.
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