dart - Dart移除 list 中的 object

Question

我想从列表中删除一个对象，但是看不到。
我想删除具有相同类型的对象，并按类型保持最大距离。

这是我的代码:

int userDistance = 851;
final String chargesJson = '''[
    {
        "type" : 1,
        "distance": 800,
        "setting": 1122,
        "bond" : 44
    },
    {
        "type" : 1,
        "distance": 850,
        "setting": 1076,
        "bond" : 50
    },
    {
        "type" : 2,
        "distance": 800,
        "setting": 1336,
        "bond" : 37
    },
    {
        "type" : 2,
        "distance": 900,
        "setting": 1299,
        "bond" : 39
    }
]
''';
final List charges = json.decode(chargesJson);

Map searchCharges(int userDistance) {
  Map result = {};

  // List all charges that are less than userDistance
  // Remove all charges that are higher
  List positiveDistanceDiff = charges.where((c) => userDistance - c['distance'] >= 0 ).toList();
  print('positiveDistanceDiff : $positiveDistanceDiff');

我有这个 :

positiveDistanceDiff : [{type: 1, distance: 800, setting: 1122, bond: 44}, {type: 1, distance: 850, setting: 1076, bond: 50}, {type: 2, distance: 800, setting: 1336, bond: 37}]

但是我只希望每种类型的对象具有最长的距离。
所以在我的例子中，我想列出一个没有

{type: 1, distance: 800, setting: 1122, bond: 44}

Answer 1

像这样吗我不确定我是否完全理解您的问题，因为按照您自己的逻辑，您还应该删除距离为800的“type:2”条目？

另外，我编写了代码，因此它创建了一个新列表，其中的值已被过滤。

import 'dart:convert';

const String chargesJson = '''[
    {
        "type" : 1,
        "distance": 800,
        "setting": 1122,
        "bond" : 44
    },
    {
        "type" : 1,
        "distance": 850,
        "setting": 1076,
        "bond" : 50
    },
    {
        "type" : 2,
        "distance": 800,
        "setting": 1336,
        "bond" : 37
    },
    {
        "type" : 2,
        "distance": 900,
        "setting": 1299,
        "bond" : 39
    }
]
''';

void main() {
  final charges = json.decode(chargesJson) as List<dynamic>;

  final filteredList = charges
      .cast<Map<String, dynamic>>()
      .fold(<int, Map<String, dynamic>>{},
          (Map<int, Map<String, dynamic>> map, element) {
        final type = element['type'] as int;

        if (!map.containsKey(type) ||
            (map[type]['distance'] as int) < (element['distance'] as int)) {
          map[type] = element;
        }

        return map;
      })
      .values
      .toList();

  filteredList.forEach(print);
  // {type: 1, distance: 850, setting: 1076, bond: 50}
  // {type: 2, distance: 900, setting: 1299, bond: 39}
}