https://stackoverflow.com/questions/48659933/add-property-dynamically-to-linqs-groupby-result/

stack.48659933.cs

//+---------------------------------+
//| Name PValue RValue NValue Group |
//+---------------------------------+
//| Low    100    600    300    Car |
//| High   900    400    700    Car |
//| Low    200    300    500   Truck|
//| High   800    700    500   Truck|
//+---------------------------------+

void Main()
{
	var kpis = new[]{
		new KPI{Group="Car", Name="Low",PersonalValue=100, RegionalValue=600, NationalValue=300},
		new KPI{Group="Car", Name="High",PersonalValue=900, RegionalValue=400, NationalValue=700},
		new KPI{Group="Truck", Name="Low",PersonalValue=200, RegionalValue=300, NationalValue=500},
		new KPI{Group="Truck", Name="High",PersonalValue=800, RegionalValue=700, NationalValue=500},
	};

	var groups = from kpi in kpis
				group kpi by kpi.Group into groupings
				let names = groupings.Select(p => p.Name)
				let pvalues = groupings.Select(p => p.PersonalValue)
				let rvalues = groupings.Select(p => p.RegionalValue)
				let nvalues = groupings.Select(p => p.NationalValue)
				select new
				{
					Key = groupings.Key,
					Names = string.Join(", ", names),
					PValues = string.Join(", ", pvalues),
					RValues = string.Join(", ", rvalues),
					NValues = string.Join(", ", nvalues),
				};

	groups.Dump();
}

public class Customer
{
	public String Code { get; set; }
    public List<KPI> KPIs { get; set; }
}

public class KPI
{
	public String Name { get; set; }
	public int PersonalValue { get; set; }
	public int RegionalValue { get; set; }
	public int NationalValue { get; set; }
	public String Group { get; set; }
}