在我提交我的答案之前，我想说的是，我同意pmatatias。
我假设您的数据集如下所示：

// This is not needed
// final Map states = {
//  "Anxiety": [],
//  "Stress": [],
//  "Involvement": [],
//  "Relaxation": [],
//  "Fatigue": []
//};

final data = [
  {
    "id": 1,
    "states": {"Anxiety": 2, "Stress": 1, "Chronic Fatigue": 1}
  },
  {
    "id": 2,
    "states": {
      "Stress": 1,
      "Fatigue": 1,
      "Involvement": 1,
      "Slight Fatigue": 2,
      "Anxiety": 5,
      "Relaxation": 2,
      "Chronic Fatigue": 3
    }
  }
];

如果不是，则必须使用json.decode。
然后从上述数据集中提取数据：

_function(List data) {
  Map<String, dynamic> _result = {};

  for (int i = 0; i < data.length; i++) {
    _result[data[i]['id'].toString()] = _addUpAndGetPercentage(
       data[i]['states'] != null ? data[i]['states'].keys.toList(): [], data[i]['states'] != null ? data[i]['states'].values.toList(): []);
  }

  return _result;
}

//Function to get percentage
_addUpAndGetPercentage(List<String> keys, List<int> data) {
  int total = 0;
  Map<String, double> _result = {};

  for (int i = 0; i < data.length; i++) {
    total += data[i];
  }
  for (int i = 0; i < data.length; i++) {
    _result[keys[i]] =
        (data[i] / total) * 100; // Multiplying by 100 not necessary you can use (data[i] / total)
  }

  return _result;
}

然后创建一个函数来排序百分比。例如我选择：

如果焦虑〉= 10%，则按1，如果焦虑〉= 25%，则按2，如果焦虑〉= 50%，则按3，否则按0

// You can change to your own parameters here
int sortPercentage(double percentage) {
  if (percentage >= 10 && percentage < 25) {
    return 1;
  } else if (percentage >= 25 && percentage < 50) {
    return 2;
  } else if (percentage >= 50) {
    return 3;
  } else {
    return 0;
  }
}

//OR

//If you use (data[i] / total)

int sortPercentage(double percentage) {
  if (percentage >= 0.1 && percentage < 0.25) {
    return 1;
  } else if (percentage >= 0.25 && percentage < 0.50) {
    return 2;
  } else if (percentage >= 0.50) {
    return 3;
  } else {
    return 0;
  }
}

最后提取数据并排序：

getFinalResult(Map<String, dynamic> data) {
  Map<String, dynamic> _result = {};
  int _length = data.entries.toList().length;

  for (int x = 0; x < _length; x++) {
    var x_data = data.entries.toList()[x];
    var x_data_length = x_data.value.entries.toList().length;

    for (int y = 0; y < x_data_length; y++) {
      var y_data = data.entries.toList()[x].value.entries.toList()[y];
      if (_result.containsKey(y_data.key)) {
        _result.update(y_data.key, (value) {
          List _list = [];
          _list.addAll(value);
          _list.add(sortPercentage(y_data.value));

          return _list;
        });
      } else {
        _result[y_data.key] = [sortPercentage(y_data.value)];
      }
    }
  }

  return _result;
}

运行代码：

void main() async {
  var midResult = _function(data);
  var finalResult = getFinalResult(midResult);

  print(finalResult);
}

输出应如下所示：

{Anxiety: [3, 2], Stress: [2, 0], Chronic Fatigue: [2, 1], Fatigue: [0], Involvement: [0], Slight Fatigue: [1], Relaxation: [1]}