javascript - Typescript:相当于 linq .GroupBy(key => key.IdItem).Select(item => item.Single());

Question

我正在尝试从 linq 到 typescript 执行相当于 .GroupBy(key => key.IdItem).Select(item => item.Single()); 的操作。

我尝试过的:

let parents = value.reduce((parents, parent) => ({
            ...ubc,
            [parent.IdItem]: [...(parents[u.IdItem] || []), parent],
        }), {}) as Array<ItemsViewModel>;


Array.prototype.map.call(parents, parent => {
    if (parents.length > 1) {
        throw new Error('The input sequence contains more than one element');
    }
    else if (!parents.length) {
        throw new Error('The input sequence is empty');
    }
    return parent[0];
});

我做错了什么？

Answer 1

你可以这样尝试——

let parentsById = 
  value.reduce((dict, parent) => {
    let { IdItem } = parent;

    dict[IdItem] = dict[IdItem] || [];
    dict[IdItem].push(parent);
    return dict;
    }, {});

let result = 
  Object.keys(parentsById)
    .map(k => {
      let parents = parentsById[k];
      if(parents.length !== 1) { throw new Error("Must contain a single item"); }
      return parents[0];
      });

<小时/>

此外，如果您只是想要唯一的父级，则可以使用可见 ID 的哈希值 --

let result = [];
let seenIds = {};

for(let parent of value) {
  let { IdItem } = parent;
  if(!seenIds[IdItem]) {
    result.push(parent);
    seenIds[IdItem] = true;
  }
}