how to get the number of repetitions from List<int>

Question

List<int> ListIdProducts = new List<int>();
var IdProductKey = from a in me.ProductKeywords where a.Keyword == item.Id select a;
 foreach (var item2 in IdProductKey)
 {
   ListIdProducts.Add(item2.Product.Value);
 }

Result is: 5 6 7 5 2 5

I need to get the following 5=3, 6=1, 7=1, 2=1

Answer 1

Use GroupBy LINQ method:

ListIdProducts
    .GroupBy(i => i)
    .Select(g => new { Value = g.Key, Count = g.Count() });