Question

Starting from a table like this:

| Code | Year |
---------------
| A01  | 2001 |
| A01  | 2002 |
| B01  | 2002 |
| C01  | 2003 |

I have to arrive to this:

| Code | Year |
---------------
| A01  | 2001 |
| B01  | 2002 |
| C01  | 2003 |

I have to group the first column (Code) and from the second (Year) I have to get the data ‘less common as possible’ compared to all the other records. I try to explain this with the example: for the code ‘A01’ I have 2 years: ‘2001’ and ‘2002’. I have to take ‘2001’ because it’s the one that not recurs in the other records. In the case that there aren’t available values ‘Year’ that not recurs in the other records, it’s good to take whatever value.

The data are in the form of array in memory and to interact with them I’m useng some LINQ queries.

Thank you in advance!
Pileggi

Answer 1

Here is the right answer (to be compared with Alex Aza’s one : filteredItemsAlexAza and filteredItemsSsithra give different results since the less common data is not also the minimum one anymore – here 2005 instead of 2001 for A01)

class Program
{
    public static void Main(string[] args)
    {
        var items = new List<Item>
        {
            new Item { Code = "A01", Year = "2005" },
            new Item { Code = "A01", Year = "2002" },
            new Item { Code = "B01", Year = "2002" },
            new Item { Code = "C01", Year = "2003" },
        };

        var filteredItemsAlexAza = items.Select(cod => cod.Code).Distinct().Select(cod => items.OrderBy(itm => itm.Year).First(itm => itm.Code == cod)).ToList();
        var filteredItemsSsithra = items
            .Select(item => new { Item = item, NbItemsWithSameYear = items.Where(i => i.Year == item.Year).Count() })
            .GroupBy(ano => ano.Item.Code)
            .Select(group => group.OrderBy(ano => ano.NbItemsWithSameYear).First().Item)
            .ToList();
    }

    public class Item
    {
        public string Code { get; set; }
        public string Year { get; set; }
    }
}