在 Flutter 中重新排列列表映射

Question

我有一个如下的列表地图：

[
data{text: hello, date: 2020-09-11}, data{text: hi, date: 2020-09-12},
data{text: why, date: 2020-09-11}, data{text: how, date: 2020-09-10},
data{text: when, date: 2020-09-11}, data{text:flutter, date: 2020-09-12}
]

而我想要得到的是这个：

{
2020-09-10 : [how], 
2020-09-11 : [hello, why, when], 
2020-09-12 : [hi, flutter]
}

我在 list<map> 和 list 之间有点困惑，我不知道如何解决这个问题。 我已经知道使用方法toSet().toList() 删除重复的东西。 有没有与此相关的方法？提前致谢。

-------------------- 以下回答后 ----------------- ------

日期 => 创建时间，文本 => 重复

 loadRepeat() async {
    DBHelperRepeat sd = DBHelperRepeat();
    var list = await sd.repeats();
    List newList = [];

    if (list[0].createTime == list[1].createTime) {
      newList.add({
        'date': list[0].createTime,
        'repeat': list[0].repeat + ',' + list[1].createTime
      });
    } else {
      newList.add({'date': list[0].createTime, 'repeat': list[0].repeat});
      newList.add({'date': list[1].createTime, 'repeat': list[1].repeat});
    }

    for (int i = 2; i < list.length; i++) {
      if (list[i].createTime == newList.last.createTime) {
        newList.last.repeat += ',' + list[i].repeat;
      } else {
        newList.add(list[i]);
      }
    }
    print(newList);
  }

这是我的 sqlite 数据库代码

repeat.dart

class Repeat {
  final String repeat;
  final String createTime;
  final int year;
  final int month;
  final int date;

  Repeat({this.repeat, this.createTime, this.year, this.month, this.date});

  Map<String, dynamic> toMap() {
    return {
      'repeat': repeat,
      'createTime': createTime,
      'year': year,
      'month': month,
      'date': date
    };
  }

  @override
  String toString() {
    return '{repeat: $repeat, createTime: $createTime, year: $year, month: $month, date: $date}';
  }
}

db_repeat.dart

class DBHelperRepeat {
  var _db;

  Future<Database> get database async {
    if (_db != null) return _db;
    _db = openDatabase(
      join(await getDatabasesPath(), 'repeats.db'),
      onCreate: (db, version) {
        return db.execute(
          "CREATE TABLE repeats(repeat TEXT, createTime TEXT, year INT, month INT, date INT)",
        );
      },
      version: 1,
    );
    return _db;
  }

  Future<void> insertRepeat(Repeat repeat) async {
    final db = await database;
    await db.insert('repeats', repeat.toMap(),
        conflictAlgorithm: ConflictAlgorithm.replace);
  }

  Future<List<Repeat>> repeats() async {
    final db = await database;
    final List<Map<String, dynamic>> maps = await db.query('repeats');

    return List.generate(maps.length, (i) {
      return Repeat(
          repeat: maps[i]['repeat'],
          createTime: maps[i]['createTime'],
          year: maps[i]['year'],
          month: maps[i]['month'],
          date: maps[i]['date']);
    });
  }

示例数据列表：

[{repeat: repeat1, createTime: 2020-09-13, year: 2020, month: 9, date: 13}]

Answer 1

也许这可以帮助你：

DBHelperRepeat sd = DBHelperRepeat();
List<Repeat> list = await sd.repeats();


list.sort((a,b)=> a.createTime.compareTo(b.createTime));


List<Repeat> newList = [];

if(list.length == 0){
      return newList;
    } else if(list.length == 1){
      newList.addAll(list);
      return newList;
    } 

    if (list[0].createTime == list[1].createTime) {
      newList.add(
        Repeat(
          createTime: list[0].createTime,
          repeat: list[0].repeat+', '+list[1].repeat,
          date: list[0].date, 
          month: list[0].month,
          year: list[0].year
        )
      );
    } else {
      newList.add(list[0]);
      newList.add(list[1]);
    }

   if(list.length < 3){
      return newList;
    }

    for (int i = 2; i < list.length; i++) {
      if (list[i].createTime == newList.last.createTime) {

        Repeat last = newList.last;
        Repeat repeat = Repeat(
          createTime: last.createTime,
          repeat: last.repeat+', ' + list[i].repeat,
          date: last.date, 
          month: last.month,
          year: last.year
        );
        newList.removeLast();
        newList.add(repeat);
      } else {
        newList.add(list[i]);
      }
    }
    newList.forEach((element) {
      print(element.createTime);
      print(element.repeat);
    });