[英]How to merge two arrays into a map using Java streams?
Lets suppose we were given the following two arrays 让我们假设我们得到了以下两个数组
String[] keys = new String[] {"a", "b", "c", "aa", "d", "b"}
int[] values = new int[] { 1 , 2 , 3 , 4 , 5 , 6 }
And by merging these 2 arrays into HashTable we get the following 通过将这两个数组合并到HashTable中,我们得到以下结果
// pseudo-code
Map<String, Integer> dictionary = new HashTable<>(
("a" => 1)
("b" => 8) // because "b" appeared in index 1 and 5
("c" => 3)
("aa" => 4)
("d" => 5)
);
How can we do this using java Lambda style? 我们怎么能用java Lambda样式做到这一点?
So far I have the following: 到目前为止,我有以下内容:
// this loops through the range given (used for index start and end)
// and sums the values of duplicated keys
tree.listMap = IntStream.range(range[0], range[1]).boxed().collect(
Collectors.toMap(i - > dictionary[i], i - > i + 1, Integer::sum, TreeMap::new)
);
However, I'd like to take 2 arrays, merge them by key and value, where value is the sum of all values for duplicated keys. 但是,我想采用2个数组,按键和值合并它们,其中value是重复键的所有值的总和。 How can we do this?
我们应该怎么做?
There you go: 你去:
Map<String,Integer> themap =
IntStream.range (0, keys.length).boxed()
.collect (Collectors.toMap(i->keys[i],
i->values[i],
Integer::sum,
TreeMap::new));
Output: 输出:
{a=1, aa=4, b=8, c=3, d=5}
This is quite similar to the snippet you posted, though, for some reason, the snippet you posted contains no reference to the keys
and values
arrays. 这与您发布的代码段非常相似,但由于某些原因,您发布的代码段不包含对
keys
和values
数组的引用。
I don't like using streams when referring to indexes, but you can use groupingBy
and summingInt
to accomplish this: 我不喜欢在引用索引时使用流,但是你可以使用
groupingBy
和summingInt
来完成这个:
Map<String, Integer> result = IntStream.range(0, keys.length)
.boxed()
.collect(
Collectors.groupingBy(
i -> keys[i],
Collectors.summingInt(i -> values[i])
)
);
Note that this works on the assumption that keys and values are both of equal length, so you may want to do some additional validation. 请注意,这可以假设键和值都具有相同的长度,因此您可能需要进行一些额外的验证。
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