main.dart

class EachTitledNameModel{
String? letterTitle;
List<String>? nameList=[];
EachTitledNameModel ({this.letterTitle, this.nameList});
}
  
List<EachTitledNameModel> getNameTitlesWithNames(List<String> nameList){
List<EachTitledNameModel> sortedNameWithTitle = [];
  nameList.sort();
for(int i = 0; i<nameList.length; i++){
  String thisTitle= nameList[i][0];
   if(sortedNameWithTitle.any((e)=> e.letterTitle== thisTitle)){
     continue;
   }
   else{
   sortedNameWithTitle.add(EachTitledNameModel(letterTitle: thisTitle,nameList: nameList.where((e)=> e[0]==thisTitle).toList()));
 }
  
}
  return sortedNameWithTitle;
}
void main() {
  getNameTitlesWithNames(childNames).forEach((e){
    print("\n${e.letterTitle!}");
    print(e.nameList);
  });
}

List<String> childNames = [
  "Olivia",
  "Liam",
  "Emma",
  "Noah",
  "Ava",
  "Isabella",
  "Sophia",
  "Mia",
  "Charlotte",
  "Amelia",
  "Harper",
  "Evelyn",
  "Abigail",
  "Emily",
  "Elizabeth",
  "Sofia",
  "Scarlett",
  "Grace",
  "Lily",
  "Avery",
  "Ella",
  "Chloe",
  "Victoria",
  "Aria",
  "Madison",
  "Layla",
  "Riley",
  "Zoe",
  "Nora",
  "Lily",
  "Ethan",
  "William",
  "James",
  "Benjamin",
  "Henry",
  "Alexander",
  "Michael",
  "Daniel",
  "Matthew",
  "Jack",
  "Samuel",
  "Joseph",
  "David",
  "Andrew",
  "Noah",
  "Oliver",
  "Lucas",
  "Mason",
  "Logan",
  "Caleb",
  "Elijah",
  "William",
  "Gabriel",
  "Jackson",
  "Owen",
  "Joseph",
  "Aiden",
  "Sebastian",
  "Julian",
  "Wyatt"
];