Working with list of tuples: calculating number of items

Question

I have the following code working with Tuples. Input is list of items, output is list of tuples and we need to calculate number of items for each date basically.

List<Tuple<DateTime, int>> list = new List<Tuple<DateTime, int>>();
foreach (ItemClass item in items)
{
    foreach(Tuple<DateTime, int> tuple in list)
    {
         if (tuple.Item1 == item.date)
         {
              tuple.Item2++;
              continue;
          }
    }
    list.Add(Tuple.Create<DateTime, int>(item.date, 1)); 
}

This code currently doesn't compile because Item2 is read-only, the question is how to make it work?

Earlier this worked with the Dictionary but I had to remove it because it was not acceptable for outer code to work with the Dictionary.

Answer 1

Tuples are not intended for use in scenarios where mutability is required. You could make your own class that combines a DateTime with a mutable integer counter, but you can also do it with LINQ, converting to a list of tuples at the very end:

var list = items
    .GroupBy(item => item.date)
    .Select(g => Tuple.Create(g.Key, g.Count()))
    .ToList();

The above code creates a group for each date, and then produces tuples only when the final counts of items in each group are known.