從具有相同屬性的多個串列創建串列-有解無憂

我的行串列：

List rowlist = [Student(name: 'John',age: 12),
             Student(name: 'Kity',age: 13),
             Student(name: 'Micle',age: 14),
             Student(name: 'Jack',age: 12),
             Student(name: 'Cha',age: 13),
             Student(name: 'Duc',age: 13),
             Student(name: 'Ran',age: 12)]

預期結果：

List result = [
               [
                Student(name: 'John',age: 12),
                Student(name: 'Jack',age: 12),
                Student(name: 'Ran',age: 12),
               ],
               [
                Student(name: 'Kity',age: 13),
                Student(name: 'Cha',age: 13),
                Student(name: 'Duc',age: 13),
               ],
               [
                Student(name: 'Micle',age: 14),
               ]
             ]

我需要創建串列的一個新的串列，其中每個串列是通過添加Student與age欄位等于。結果的最佳方式是什么？

uj5u.com熱心網友回復：

如果使用收藏包。您可以使用該groupListsBy方法將所有學生按年齡分組。

Map<int, List<Student>> result = rowlist.groupListsBy((student) => student.age);

但是，以上將資料作為Map<int, List<Student>. 您可以List<List<Student>>通過呼叫將其轉換為 a .values.toList()。

List<List<Student>> result = rowlist.groupListsBy((student) => student.age).values.toList();

完整示例：

import 'package:collection/collection.dart';

void main() {
  List<Student> rowlist = [
    Student(name: 'John', age: 12),
    Student(name: 'Kity', age: 13),
    Student(name: 'Micle', age: 14),
    Student(name: 'Jack', age: 12),
    Student(name: 'Cha', age: 13),
    Student(name: 'Duc', age: 13),
    Student(name: 'Ran', age: 12),
  ];

  List<List<Student>> result =
      rowlist.groupListsBy((student) => student.age).values.toList();

  print(result);
}

class Student {
  final String name;
  final int age;
  const Student({required this.name, required this.age});
  @override
  String toString() => 'Student(name: $name, age: $age)';
}

uj5u.com熱心網友回復：

您也可以在沒有任何包的情況下執行此操作。

List rowlist = [
  Student(name: 'John', age: 12),
  Student(name: 'Kity', age: 13),
  Student(name: 'Micle', age: 14),
  Student(name: 'Jack', age: 12),
  Student(name: 'Cha', age: 13),
  Student(name: 'Duc', age: 13),
  Student(name: 'Ran', age: 12)
];

void main() {
  Map<int, List<Student>> groupMap = {};

  for (final s in rowlist) {
    if (groupMap.containsKey(s.age)) {
      groupMap[s.age]!.add(s);
    } else {
      groupMap[s.age] = [s];
    }
  }

  final result = groupMap.entries.map((e) => e.value).toList();
  
  print(result);
}

class Student {
  Student({required this.name, required this.age});
  final String name;
  final int age;

  @override
  String toString() => '$name - $age';
}

轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/395288.html

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