Group by multiple fields and get max value using Dart and Flutter - flutter

Question

I am new to dart, I have a requirement to group by multiple fields and get the minimum value of each student. I don't have an idea on how to implement since I am new in dart. Below is the example of the realtime firebase table structure.
"gameRanking" : {
"-MmvcDgrGsuCjhcsmXfP" : {
"game" : "Puzzle",
"score" : "105",
"student" : "John Doe",
},
"-MasdDgrGsuCjhcsmXfP" : {
"game" : "Puzzle",
"score" : "99",
"student" : "John Doe",
},
"-Mmw0kagqLrEbdWlkXg7" : {
"game" : "Puzzle",
"score" : "87",
"student" : "Mary Doe",
},
"-MmwC8ONbJUWzP_Wa7X0" : {
"game" : "Puzzle",
"score" : "95",
"student" : "Mary Doe",
}
},
Here is the expected output:
Puzzle John Doe 99
Puzzle Mary Doe 87

Answer 1

I won't answer the question entirely because it's clearly a "do my homework" kind of question.
But in order to assist you in getting started with programming, I thought it would be useful to post "nearly" the whole solution here. I hope you will be able to then read answers in other related questions, for example this one, to get to the final solution.
Here you go, this solves the "plumbing" part of the problem:
class Stats {
String game;
int score;
String student;
Stats(this.game, this.score, this.student);
#override
String toString() => "Stats($game, $score, $student)";
}
main() {
final map = {
"gameRanking": {
"-MmvcDgrGsuCjhcsmXfP": {
"game": "Puzzle",
"score": "105",
"student": "John Doe",
},
"-MasdDgrGsuCjhcsmXfP": {
"game": "Puzzle",
"score": "99",
"student": "John Doe",
},
"-Mmw0kagqLrEbdWlkXg7": {
"game": "Puzzle",
"score": "87",
"student": "Mary Doe",
},
"-MmwC8ONbJUWzP_Wa7X0": {
"game": "Puzzle",
"score": "95",
"student": "Mary Doe",
}
},
};
final rankingsById = map["gameRanking"] ?? {};
final rankings = rankingsById.map((id, data) {
return MapEntry(
id,
Stats(data["game"].coerceToString(), data["score"].coerceToInt(),
data["student"].coerceToString()));
}).values;
rankings.forEach((stats) => print(stats));
}
extension on Object? {
int coerceToInt() => int.parse(coerceToString());
String coerceToString() => this?.toString() ?? "?";
}
Running this prints:
Stats(Puzzle, 105, John Doe)
Stats(Puzzle, 99, John Doe)
Stats(Puzzle, 87, Mary Doe)
Stats(Puzzle, 95, Mary Doe)
Good luck finishing the rest of the owl :)

Answer 2

I needed the same... I don't know if this is the best solution...
Map<int,List<MyObject>> mom=groupBy(_myObjectList,(element)=>element.cornerCnt);//get a Map with cornerCnt as key and a List of myObjects for every key
int maxCornerCnt;
int max=0;
mom.forEach((key, moList) { //for every map entry
int len=moList.length; //get lenght of myObject-list
if (len>max) {
max=len;
maxCornerCnt=key; //write key(cornerCnt) to maxCornerCnt
}
});