How get a statistical summary from List of Maps in Dart?-CodePudding

Using the following List of Maps, I would like to create a kind of statistical summary in order to be able to create a plot from it.

    List<dynamic> data = [
  {
    "SoftwareVersion": "10.09.21",
    "Controller": "P1",
  },
  {
    "SoftwareVersion": "11.11.03",
    "Controller": "P1",
  },
  {
    "SoftwareVersion": "11.11.03",
    "Controller": "P2",
  },
  {
    "SoftwareVersion": "28.09.04",
    "Controller": "P2",
  },
  {
    "SoftwareVersion": "28.09.04",
    "Controller": "P2",
  },
  {  
    "SoftwareVersion": "28.09.04",
    "Controller": "P3",  
  }];

The expected outcome from the list above should look like the list below. So that for each available controller I get a count for the actual used SoftwareVersion.

List newData = [
{
  "P1": {
    "10.09.21": 1,
    "11.11.03": 1,
    },
  "P2": {
    "11.11.03": 1,
    "28.09.04": 2
    },
  "P3": {
    "28.09.04": 1
    } 
}];

CodePudding user response：

Just iterate over the list adding to the newData map. Be careful to add an empty value if this controller or version hasn't been seen before - use the handy putIfAbsent for that. (Note that I removed the unnecessary outer list from newData);

void main() {
  data.forEach(addToNewData);
  print(newData);
}

void addToNewData(Map<String, String> e) {
  final version = e['SoftwareVersion']!;
  final controller = e['Controller']!;
  final controllerMap = newData.putIfAbsent(controller, () => <String, int>{});
  controllerMap[version] = controllerMap.putIfAbsent(version, () => 0)   1;
}

final newData = <String, Map<String, int>>{};