[英]Converting a nested HashMap with a list to another nested HashMap with a linkedHashMap instead of the list
I have a map in java that is an instance of the following:我在 java 中有一个 map,它是以下示例:
Map< K1,Map< K2, List<Object>>>
I want to convert it to the following structure:我想将其转换为以下结构:
Map< K1, Map< K2, LinkedHashMap<Object, Value>>>
Where Value is a property of Object.其中 Value 是 Object 的属性。 I also want to preserve the order in the list to the HashMap.我还想将列表中的顺序保留到 HashMap。
I found some similar code examples of what i am trying to achieve but not the same.我发现了一些我想要实现的类似代码示例,但不一样。 I appreciate any help i can get.我很感激我能得到的任何帮助。
Please try this.请试试这个。 Assume the first map is foo
and the second map (with LinkedHashMap) is bar
.假设第一个 map 是foo
而第二个 map (带有 LinkedHashMap)是bar
。
bar = new HashMap<>();
for (var key1 : foo.keySet()) {
bar.put(key1, new HashMap<>()); // key1 is of type K1
var innerMap = foo.get(key1); // type: Map< K2, List<Object>>
for (var key2 : innerMap.keySet()) { // key2 is of type K2
bar.get(key1).put(key2, new LinkedHashMap<>());
var innerLinkedMap = bar.get(key1).get(key2); // type: LinkedHashMap<Object, Value>; now empty
for (var element : innerMap.get(key2)) {
innerLinkedMap.put(element, element.something); // insert in the order of the list
}
}
}
Note that it only works if the elements in each list are unique, otherwise the same key would be re-inserted into the LinkedHashMap, which does not affect the insertion order.请注意,它仅在每个列表中的元素都是唯一的情况下才有效,否则相同的键将重新插入到 LinkedHashMap 中,这不会影响插入顺序。
I may make some silly mistake in the implementation above, please do comment and edit in that case.我可能在上面的实现中犯了一些愚蠢的错误,请在这种情况下进行评论和编辑。
It can be done using streams可以使用流来完成
map.entrySet().stream().collect(toMap(
Map.Entry::getKey, // K1
//transforming inner map
e -> e.getValue().entrySet().stream().collect(toMap(
Map.Entry::getKey, // K2
// iterating list and transforming it into linkedhashmap
es -> es.getValue().stream().collect(
toMap(identity(),
Obj::getValue,
(a, b) -> b,
LinkedHashMap::new)
)
))
));
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