flutter - 如何从DART/Flutter中的数组中获取按天分组的每天的值总和？

Question

您好，如何获取按createdTime日分组的对象列表下面的isWatch属性的总和？

[
  {
    "videoId": 1,
    "videoName": "Test Video 1",
    "duration": 300,
    "createdTime": "1969-07-20 20:18:04Z",
    "isWatch": 1,
  },
  {
    "videoId": 2,
    "videoName": "Test Video 2",
    "duration": 500,
    "createdTime": "1969-07-20 20:18:04Z",
    "isWatch": 10,
  }
]

Answer 1

(针对阿米特·库马尔的评论进行了编辑)

我认为最简单的方法是:

    import "package:collection/collection.dart";

    List<Map<String, dynamic>> liste = [
    {
      "videoId": 1,
      "videoName": "Test Video 1",
      "duration": 300,
      "createdTime": "1969-07-20 20:18:04Z",
      "isWatch": 1,
    },
    {
      "videoId": 2,
      "videoName": "Test Video 2",
      "duration": 500,
      "createdTime": "1969-07-20 20:18:04Z",
      "isWatch": 10,
    },
    {
      "videoId": 2,
      "videoName": "Test Video 2",
      "duration": 500,
      "createdTime": "1969-07-21 20:18:04Z",
      "isWatch": 13,
    },
    {
      "videoId": 2,
      "videoName": "Test Video 2",
      "duration": 500,
      "createdTime": "1969-07-23 20:18:04Z",
      "isWatch": 12,
    },
    {
      "videoId": 2,
      "videoName": "Test Video 2",
      "duration": 500,
      "createdTime": "1969-07-23 20:18:04Z",
      "isWatch": 14,
    }
  ];

  _groupAndSum() {
    Map groupByDay =
        groupBy(liste, (obj) => DateTime.parse(obj['createdTime'].split(' ')[0])));

    Map groupedAndSum = Map();

    groupByDay.forEach((k, v) {
      groupedAndSum[k] = {
        'list': v,
        'sumOfisWatch': v.fold(0, (prev, element) => prev + element['isWatch']),
      };
    });

    print(groupByDay.toString());
    print(groupedAndSum.toString());
  }

输出将是:

flutter: {20: [{videoId: 1, videoName: Test Video 1, duration: 300, createdTime: 1969-07-20 20:18:04Z, isWatch: 1}, {videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-20 20:18:04Z, isWatch: 10}], 21: [{videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-21 20:18:04Z, isWatch: 13}], 23: [{videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-23 20:18:04Z, isWatch: 12}, {videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-23 20:18:04Z, isWatch: 14}]}

flutter: {20: {list: [{videoId: 1, videoName: Test Video 1, duration: 300, createdTime: 1969-07-20 20:18:04Z, isWatch: 1}, {videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-20 20:18:04Z, isWatch: 10}], sumOfisWatch: 11}, 21: {list: [{videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-21 20:18:04Z, isWatch: 13}], sumOfisWatch: 13}, 23: {list: [{videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-23 20:18:04Z, isWatch: 12}, {videoId: 2, videoName: Test Video 2, duration: 500, createdTime: 1969-07-23 20:18:04Z, isWatch: 14}], sumOfisWatch: 26}}