groupby 和 select 来自本机对象的最大 id

Question

如何 groupby 和 select 在 React Native 中从对象获取最大 ID。那只是一个虚拟数据，用于向您解释我的对象的外观

[
 {"name": "alex", "subject": "english" "student_id": "1"},
 {"name": "hales", "subject": "science" "student_id": "2"},
 {"name": "joss", "subject": "english" "student_id": "3"},
 {"name": "alexandra", "subject": "science" "student_id": "4"},
 {"name": "mark", "subject": "math" "student_id": "5"},
]

首先，我想按学科分组，然后 select 具有最大 ID 的学生，所以我的输出应该是这样的

[
 {"name": "joss", "subject": "english" "student_id": "3"},
 {"name": "alexandra", "subject": "science" "student_id": "4"},
 {"name": "mark", "subject": "math" "student_id": "5"},
]

到目前为止我已经尝试过的是

const result = myobject.reduce(function (r, a) {
      r[a.case_id] = r[a.case_id] || [];
      r[a.case_id].push(a);
      return r;
    }, Object.create(null));

使用上面的代码我可以分组但无法获得最大 ID 那么我该如何实现呢？

Answer 1

您可以按 subject 分组，如果 student_id 更大，则替换该值。

作为结果从对象中获取值。

const
    data = [{ name: "alex", subject: "english", student_id: "1" }, { name: "hales", subject: "science", student_id: "2" }, { name: "joss", subject: "english", student_id: "3" }, { name: "alexandra", subject: "science", student_id: "4" }, { name: "mark", subject: "math", student_id: "5" }],
    result = Object.values(data.reduce((r, o) => {
        if (!r[o.subject] || +r[o.subject].student_id < +o.student_id) {
            r[o.subject] = o;
        }
        return r;
    }, Object.create(null)));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 2

lodash 如果不介意的话。这似乎是一种简洁明了的理解方式

const data = [{ name: "alex", subject: "english", student_id: "1" }, { name: "hales", subject: "science", student_id: "2" }, { name: "joss", subject: "english", student_id: "3" }, { name: "alexandra", subject: "science", student_id: "4" }, { name: "mark", subject: "math", student_id: "5" }];

const result = _.chain(data)
  .groupBy('subject')
  .values()
  .map((group) => _.maxBy(group, 'student_id'))
  .value();
  
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js" integrity="sha512-WFN04846sdKMIP5LKNphMaWzU7YpMyCU245etK3g/2ARYbPK9Ub18eG+ljU96qKRCWh+quCY7yefSmlkQw1ANQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

groupby 和 select 来自本机对象的最大 id

groupby and select max id from object in react native

javascript

group-by

object

react-native