如何从列表 Dart 中删除重复项 |扑

Question

我有一套物品。从这里我想删除所有重复的值。我试过这个 finalList = [...{...users!}]; 和这个print(users.toSet().toList());。但两者都在打印列表中的所有数据。它没有删除重复的值。以下是我的清单

List users = [
    {
      "userEmail":"tintu@gmail.com"
    },
    {
      "userEmail":"john@gmail.com"
    },
    {
      "userEmail":"tintu@gmail.com"
    },
    {
      "userEmail":"rose@gmail.com"
    },
    {
      "userEmail":"john@gmail.com"
    },
  ];

预期输出

List users = [
    {
      "userEmail":"tintu@gmail.com"
    },
    {
      "userEmail":"john@gmail.com"
    },
    {
      "userEmail":"rose@gmail.com"
    },
  ];

Answer 1

让我们试试，这里你得到唯一列表

void main() {
  var users = [
    {"userEmail": "tintu@gmail.com"},
    {"userEmail": "john@gmail.com"},
    {"userEmail": "tintu@gmail.com"},
    {"userEmail": "rose@gmail.com"},
    {"userEmail": "john@gmail.com"},
  ];
  var uniqueList = users.map((o) => o["userEmail"]).toSet();
  print(uniqueList.toList());
}

Answer 2

您的尝试不起作用，因为大多数对象（包括Map）使用== 运算符的默认实现，它只检查对象身份。请参阅：How does a set determine that two objects are equal in dart? 和 How does Dart Set compare items?。

使List 到Set 到List 方法起作用的一种方法是明确指定Set 应如何比较对象：

import 'dart:collection';

void main() {
  var users = [
    {"userEmail": "tintu@gmail.com"},
    {"userEmail": "john@gmail.com"},
    {"userEmail": "tintu@gmail.com"},
    {"userEmail": "rose@gmail.com"},
    {"userEmail": "john@gmail.com"},
  ];

  var finalList = [
    ...LinkedHashSet<Map<String, String>>(
      equals: (user1, user2) => user1['userEmail'] == user2['userEmail'],
      hashCode: (user) => user['userEmail'].hashCode,
    )..addAll(users)
  ];
  finalList.forEach(print);
}