如何统计嵌套数组中detail.id或groupDocs.id的唯一值？

需求 #

统计初始数据data中detail.id的唯一数量，或者数组处理结果groupDocs中groupDocs.id的唯一数量。

无效尝试代码 #

const v1 = new Set(data.map(i => i.details.id))
console.log("v1: ", v1);

const v2 = [...new Set(groupDocs)];
console.log("v2: ", v2);

const v3 = data.reduce((total, el) => {
  el.details.forEach((el) => {
    if (el in total) total[el]++;
    else total[el] = 1;
  });
  return total;
}, {});

console.log("v3: ", v3);

完整代码（含原始数据、分组逻辑及无效尝试） #

const data = [
  {
    id: 222222,
    document_file_name: "4020653_FileName.pdf",
    document_url: "www.",
    document_updated_at: "2020-07-08T19:41:28.385Z",
    document_type_label: "doc label",
    state: "accepted",
    details: [
      {
        id: 20656,
        type: "Claimant",
        name: "First Name Last Name",
        first_name: "First Name",
        last_name: "Last Name",
        type_label: "claimant"
      },
      {
        id: 20657,
        type: "Fellow",
        name: "Fellow First Name Fellow Last Name",
        first_name: "Fellow First Name",
        last_name: "Fellow Last Name",
        type_label: "fellow"
      }
    ]
  },
  {
    id: 1111111,
    document_file_name: "4020600_FileName.pdf",
    document_url: "www.",
    document_updated_at: "2020-07-08T19:41:28.385Z",
    document_type_label: "doc label",
    state: "rejected",
    details: [
      {
        id: 2000,
        type: "Fellow",
        name: "Fellow First Name Fellow Last Name",
        first_name: "Fellow First Name",
        last_name: "Fellow Last Name",
        type_label: "fellow"
      },
      {
        id: 20656,
        type: "Claimant",
        name: "First Name Last Name",
        first_name: "First Name",
        last_name: "Last Name",
        type_label: "claimant"
      }
    ]
  },
  {
    id: 333333,
    document_file_name: "4020890_FileName.pdf",
    document_url: "www.",
    document_updated_at: "2020-07-08T19:41:28.385Z",
    document_type_label: "doc label",
    state: "rejected",
    details: [
      {
        id: 20657,
        type: "Fellow",
        name: "Fellow First Name Fellow Last Name",
        first_name: "Fellow First Name",
        last_name: "Fellow Last Name",
        type_label: "fellow"
      }
    ]
  },
  {
    id: 444444,
    document_file_name: "4020672_FileName.pdf",
    document_url: "www.",
    document_updated_at: "2020-07-08T19:41:28.385Z",
    document_type_label: "doc label",
    state: "rejected",
    details: [
      {
        id: 20657,
        type: "Fellow",
        name: "Other",
        first_name: "First Name",
        last_name: "Last Name",
        type_label: "claimant"
      }
    ]
  }
];

const groupDocs = [
  ...data
    .reduce(
      (
        travelDocsMap,
        {
          id: travel_doc_id,
          document_file_name,
          document_type_label,
          document_url,
          state,
          details = []
        }
      ) => {
        let details_ids = details.map((o) => o.id).sort();
        const details_ids_unique = details_ids.join("_"),
          type = details.map((o) => o.type),
          name = details.map((o) => o.name);
        if (details_ids.length === 1) {
          details_ids = details_ids[0];
        }

        const details_g = travelDocsMap.get(details_ids_unique) ?? {
          id: details_ids,
          type,
          name,
          docs: []
        };
        details_g.docs.push({
          travel_doc_id,
          document_file_name,
          document_type_label,
          document_url,
          state
        });
        travelDocsMap.set(details_ids_unique, details_g);
        return travelDocsMap;
      },
      new Map()
    )
    .values()
];
console.log("groupDocs: ", groupDocs);

const v1 = new Set(data.map(i => i.details.id))
console.log("v1: ", v1);

const v2 = [...new Set(groupDocs)];
console.log("v2: ", v2);

const v3 = data.reduce((total, el) => {
 el.details.forEach((el) => {
  if (el in total) total[el]++;
  else total[el] = 1;
});
return total;
}, {});

console.log("v3: ", v3);

有效解决方案 #

方法1：从原始data中统计唯一detail.id #

利用flatMap扁平化所有details数组，提取每个detail.id后存入Set自动去重，最后通过size属性获取数量：

const uniqueDetailIds = new Set(data.flatMap(item => item.details.map(detail => detail.id)));
console.log("唯一detail.id数量：", uniqueDetailIds.size); // 输出：3

方法2：从groupDocs中统计唯一id #

注意groupDocs中的id可能是单个数字或数组（当原details包含多个元素时），需要先将数组展开，再存入Set：

const uniqueGroupIds = new Set(
  groupDocs.flatMap(item => Array.isArray(item.id) ? item.id : [item.id])
);
console.log("唯一groupDocs.id数量：", uniqueGroupIds.size); // 输出：3

无效尝试的问题分析 #

• v1错误原因：data.map(i => i.details.id)中i.details是数组，没有id属性，最终得到的是一组undefined，无法统计有效id。
• v2错误原因：直接将groupDocs中的对象存入Set，每个对象都是独立引用，Set无法识别重复的id值，只能判断对象引用是否相同。
• v3错误原因：用整个detail对象作为统计键，对象会被转为字符串[object Object]，所有统计项都会被归为同一个键，最终统计的是总数量而非唯一id数量。

内容的提问来源于stack exchange，提问作者user1128912