javascript LoDash - 如何通过公共键将一个集合值推送到另一个集合中
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LoDash - How to push one collections values into another via common key
提问by webmaster_sean
I have two collections.
我有两个收藏。
var a =
[
{unique_id: "001", state: "CO"},
{unique_id: "001", state: "TX"},
{unique_id: "001", state: "CC"},
{unique_id: "002", state: "CC"},
{unique_id: "002", state: "NY"}
]
And
和
var b =
[
{unique_id: "001", states:[]},
{unique_id: "002", states:[]}
]
And I want to get:
我想得到：
var b =
[
{unique_id: "001", states:["CO","TX","CC"]},
{unique_id: "002", states:["CC","NY"]}
]
I should mention that the "b" array has to stay in the same order it's in AND some of the unique_id's don't have a value.
我应该提到“b”数组必须保持与它所在的顺序相同，并且一些 unique_id 没有值。
I've been trying to use LoDash https://lodash.com/- so if anyone can solve this with LoDash that would be awesome!
我一直在尝试使用 LoDash https://lodash.com/- 所以如果有人能用 LoDash 解决这个问题，那就太棒了！
回答by Pavan Ravipati
The time complexity of this solution is suboptimal ( O(n^2) ), but it might help you think of ways to match pushing the values into "b":
这个解决方案的时间复杂度是次优的（ O(n^2) ），但它可能会帮助你想出匹配将值推入“b”的方法：
_.forEach(a, function(element1){
_.forEach(b, function(element2){
if (element2.unique_id === element1.unique_id) {
element2.states.push(element1.state);
}
});
});
Perhaps a better solution might be to index your objects in b by their unique id using lodash's _.indexBymethod. For example you can index your objects in b as follows:
也许更好的解决方案可能是使用 lodash 的_.indexBy方法通过它们的唯一 id 索引 b 中的对象。例如，您可以按如下方式在 b 中索引您的对象：
var c = _.indexBy(b, 'unique_id')
Which will result in:
这将导致：
{001:{unique_id: "001", states:[]}, 002: {unique_id: "002", states:[]}}
Since the objects in our c array are pointing to the same objects in memory as those in our b array, we can directly mutate our objects in c and b will reference those updated objects in memory. So:
由于 c 数组中的对象与 b 数组中的对象指向内存中的对象相同，因此我们可以直接改变 c 中的对象，b 将引用内存中更新的对象。所以：
_.forEach(a, function(element1){
if (element1.unique_id in c) {
c[element1.unique_id].states.push(element1.state);
}
})
Now if we take a look at our b array, we'll see that the value is:
现在，如果我们看看我们的 b 数组，我们会看到它的值是：
var b =
[
{unique_id: "001", states:["CO","TX","CC"]},
{unique_id: "002", states:["CC","NY"]}
]
The time complexity of this solution should be close to O(n), which is much better than using the nested _.forEachapproach. Code snippet:
这个解决方案的时间复杂度应该接近 O(n)，这比使用嵌套的_.forEach方法要好得多。代码片段：
var a =
[
{unique_id: "001", state: "CO"},
{unique_id: "001", state: "TX"},
{unique_id: "001", state: "CC"},
{unique_id: "002", state: "CC"},
{unique_id: "002", state: "NY"}
];
var b =
[
{unique_id: "001", states:[]},
{unique_id: "002", states:[]}
];
var c = _.indexBy(b, 'unique_id');
_.forEach(a, function(element1){
if (element1.unique_id in c) {
c[element1.unique_id].states.push(element1.state);
}
});
document.writeln(JSON.stringify(b))<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.9.3/lodash.js"></script>回答by Adam Boduch
groupBy()and map()are your friends:
_(a).groupBy('unique_id')
.map(function(item, key) {
return {
unique_id: key,
states: _.pluck(item, 'state')
};
})
.value()
You're basically grouping the states by their unique_id, then mapping that object to an array where each item has the structure you need.
您基本上是按状态对状态进行分组unique_id，然后将该对象映射到一个数组，其中每个项目都具有您需要的结构。
