Question

I need to split a list into multiple lists that are grouped according to the first character of a string property. Here’s an example.

class Program
{
    static void Main(string[] args)
    {
        var makes = new List<VehicleMake>
                        {
                            new VehicleMake {Name = "Acura"},
                            new VehicleMake {Name = "AMG"},
                            new VehicleMake {Name = "Audi"},
                            new VehicleMake {Name = "BMW"},
                            new VehicleMake {Name = "Chevrolet"},
                            new VehicleMake {Name = "Datsun"},
                            new VehicleMake {Name = "Eagle"},
                            new VehicleMake {Name = "Fiat"},
                            new VehicleMake {Name = "Honda"},
                            new VehicleMake {Name = "Infiniti"},
                            new VehicleMake {Name = "Jaguar"}
                        };

        var balancedLists = makes.Balance(new List<BalancedListGroup>
                          {
                              new BalancedListGroup { RangeStart = 'A', RangeEnd = 'C'},
                              new BalancedListGroup { RangeStart = 'D', RangeEnd = 'F'},
                              new BalancedListGroup { RangeStart = 'G', RangeEnd = 'J'},
                          });

        foreach (var balancedList in balancedLists)
        {
            foreach (var vehicleMake in balancedList)
            {
                Console.WriteLine(vehicleMake.Name);
            }
            Console.WriteLine("---");
        }
        Console.ReadLine();
    }
}

public class VehicleMake
{
    public string Name { get; set; }
}

public static class VehicleMakeListBalancer
{
    public static List<List<VehicleMake>> Balance(this List<VehicleMake> list, List<BalancedListGroup> groups)
    {
        var letters =
            new List<string> { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "y", "z" };
        var balancedLists = new List<List<VehicleMake>>();
        foreach (var group in groups)
        {
            var groupList = new List<VehicleMake>();
            for (var i = letters.IndexOf(group.RangeStart.ToString().ToLower()); i <= letters.IndexOf(group.RangeEnd.ToString().ToLower()); i++)
            {
                groupList.AddRange(list.Where(l => l.Name.ToLower().StartsWith(letters[i].ToString())).ToList());
            }
            balancedLists.Add(groupList);
        }

        return balancedLists;
    }
}

public class BalancedListGroup
{
    public char RangeStart { get; set; }
    public char RangeEnd { get; set; }
}

Which outputs:

Acura
AMG
Audi
BMW
Chevrolet
---
Datsun
Eagle
Fiat
---
Honda
Infiniti
Jaguar
---

This algorithm works, but feels very clumsy. Is there a more elegant way to do this?

Answer 1

Following extention method uses linq to select all the vehicle makes whose name starts in range of characters.

        public static List<VehicleMake> GetInRange(this List<VehicleMake> vehicleList, char RangeStart, char RangeEnd)
        {
            var vehiclesInRange = from vm in vehicleList
                                  where vm.Name[0] >= RangeStart && vm.Name[0] <= RangeEnd
                                  select vm;

            return vehiclesInRange.ToList();
        }

USAGE SAMPLE

    static class Program
    {
        static void Main(string[] args)
        {
            var makes = new List<VehicleMake> { 
                new VehicleMake { Name = "Acura" },
                new VehicleMake { Name = "AMG" },
                new VehicleMake { Name = "Audi" }, 
                new VehicleMake { Name = "BMW" }, 
                new VehicleMake { Name = "Chevrolet" },
                new VehicleMake { Name = "Datsun" },
                new VehicleMake { Name = "Eagle" }, 
                new VehicleMake { Name = "Fiat" },
                new VehicleMake { Name = "Honda" }, 
                new VehicleMake { Name = "Infiniti" },
                new VehicleMake { Name = "Jaguar" } 
            }; 


            var atoc =  makes.GetInRange('A', 'C');
            atoc.Print();

            var dtom = makes.GetInRange('D', 'M');
            dtom.Print();

            var mtoz = makes.GetInRange('M', 'Z');
            mtoz.Print();

            Console.ReadLine();
        }

        static List<VehicleMake> GetInRange(this List<VehicleMake> vehicleList, char RangeStart, char RangeEnd)
        {
            var vehiclesInRange = from vm in vehicleList
                                  where vm.Name[0] >= RangeStart && vm.Name[0] <= RangeEnd
                                  select vm;

            return vehiclesInRange.ToList();
        }

        static void Print(this List<VehicleMake> vehicles)
        {
            Console.WriteLine();
            vehicles.ForEach(v => Console.WriteLine(v.Name));
        }
    }