Flutter 如何对数据图进行排序和分组

Question

我正在从 api 检索数据映射，如下所示

{
    "success": true,
    "data": {
        "items": [
            {
                "sequenceno": 1933,
                "_id": "5eff1",
                "chapter": "Numbers and Numeration",
                "title": "Place Value: 3-digits",
                "package_description": "This learning module helps to familiarise with the concept of place value of 3-digit numbers.",
                "age_level": [
                    99,
                    8
                ],
                "pkg_sequence": "2501",
                "packagescors": {
                    "score": [
                        50
                    ],
                    "date": [
                        "1600259121340"
                    ]
                }
            },
            {
                "sequenceno": 1933,
                "_id": "5d79",
                "chapter": "Numbers and Numeration",
                "title": "Place Value: 4-digits",
                "package_description": "This learning module helps the kids familiarise with the concept of Place value of a number.",
                "age_level": [
                    99,
                    8
                ],
                "pkg_sequence": "2501",
                "packagescors": {
                    "score": [
                        60
                    ],
                    "date": [
                        "1615283866457"
                    ]
                }
            },
        ]

我的目标是使用关键的“章节”对它们进行排序和分组。如下所示

           Numbers and Numeration : { // chapter name 
                    "sequenceno": 1933,
                    "_id": "5d79",
                    "chapter": "Numbers and Numeration",
                    "title": "Place Value: 4-digits",
                    "package_description": "This learning module helps the kids familiarise with the concept of Place value of a number.",
                    "age_level": [
                        99,
                        8
                    ],
                    "pkg_sequence": "2501",
                    "packagescors": {
                        "score": [
                            60
                        ],
                        "date": [
                            "1615283866457"
                        ]
 {
                    "sequenceno": 1933,
                    "_id": "5eff1",
                    "chapter": "Numbers and Numeration",
                    "title": "Place Value: 3-digits",
                    "package_description": "This learning module helps to familiarise with the concept of place value of 3-digit numbers.",
                    "age_level": [
                        99,
                        8
                    ],
                    "pkg_sequence": "2501",
                    "packagescors": {
                        "score": [
                            50
                        ],
                        "date": [
                            "1600259121340"
                        ]
                    }
                    }

与此类似，还有多个章节。那么如何对它们进行分组，以便章节名称在前，然后章节的所有相关值都在该组下？获取值的正确方法是什么

** 更新：-我正在尝试使用 for 循环来遍历数据。我想要做的是，如果密钥存在，则相应地对数据进行分组以添加密钥

Map<Item,dynamic> sortedTable = {};

Iterable<Map<String, dynamic>> data =  subjectModules.map((e) => e.toMap());
    for (var map in data) {
      try{
        if(sortedTable.containsKey(map['chapter'])){ // if key exists
             // need to add and data group it
            
        }else{ // if not
          sortedTable.putIfAbsent(map['chapter'], () => map); // i need add only keys
        }
      }catch(e){
          print('Error $e');
      }
    }

如何正确迭代和分组？

Answer 1

我使用List.forEach 方法和Map.putIfAbsent 按章节名称创建了组列表。

  final resp = {
    "data": {
      "items": [
        {
          "sequenceno": 1933,
          "_id": "5eff1",
          "chapter": "Numbers and Numeration",
          "title": "Place Value: 3-digits",
          "package_description":
              "This learning module helps to familiarise with the concept of place value of 3-digit numbers.",
          "age_level": [99, 8],
          "pkg_sequence": "2501",
          "packagescors": {
            "score": [50],
            "date": ["1600259121340"]
          }
        },
        {
          "sequenceno": 1933,
          "_id": "5d79",
          "chapter": "Numbers and Numeration",
          "title": "Place Value: 4-digits",
          "package_description":
              "This learning module helps the kids familiarise with the concept of Place value of a number.",
          "age_level": [99, 8],
          "pkg_sequence": "2501",
          "packagescors": {
            "score": [60],
            "date": ["1615283866457"]
          }
        },
        {
          "sequenceno": 1933,
          "_id": "5d79",
          "chapter": "Numbers Numeration",
          "title": "Place Value: 4-digits",
          "package_description":
              "This learning module helps the kids familiarise with the concept of Place value of a number.",
          "age_level": [99, 8],
          "pkg_sequence": "2501",
          "packagescors": {
            "score": [60],
            "date": ["1615283866457"]
          }
        },
      ]
    }
  };

  final ans = {};

  resp["data"]?["items"]?.forEach((e) {
    final entry = ans.putIfAbsent(e["chapter"], () => []);
    entry.add(e);
  });

  print(ans);

您也可以使用collection 包中的groupBy 方法。