Question

I’m having trouble with getting a my linq query correct. I’ve been resisting doing this with foreach loops because I’m trying to better understand linq.

I have following data in LinqPad.

void Main()
{
    var events = new[] {
        new {ID = 1, EventLevel = 1, PatientID = "1", CodeID = "2", Occurences = 0 },
        new {ID = 2, EventLevel = 2, PatientID = "1", CodeID = "2", Occurences = 0 },
        new {ID = 3, EventLevel = 1, PatientID = "2", CodeID = "1", Occurences = 0 },
        new {ID = 4, EventLevel = 3, PatientID = "2", CodeID = "2", Occurences = 0 },
        new {ID = 5, EventLevel = 1, PatientID = "3", CodeID = "3", Occurences = 0 },
        new {ID = 6, EventLevel = 3, PatientID = "1", CodeID = "4", Occurences = 0 }
    };

    var filter = new FilterCriterion();
    var searches = new List<FilterCriterion.Occurence>();
    searches.Add(new FilterCriterion.Occurence() { CodeID = "1", MinOccurences = 2, MaxOccurences = 3 });
    searches.Add(new FilterCriterion.Occurence() { CodeID = "2", MinOccurences = 2, MaxOccurences = 3 });

    filter.Searches = searches;

    var summary = from e in events
        let de = new
        {
            PatientID = e.PatientID,
            CodeID = e.CodeID
        }
        group e by de into t
        select new
        {
            PatientID = t.Key.PatientID,
                CodeID = t.Key.CodeID,
            Occurences = t.Count(d => t.Key.CodeID == d.CodeID)
        };

    var allCodes = filter.Searches.Select(i => i.CodeID);

    summary = summary.Where(e => allCodes.Contains(e.CodeID));

    // How do I find the original ID property from the "events" collection and how do I 
    // eliminate the instances where the Occurences is not between MinOccurences and MaxOccurences.

    foreach (var item in summary)
        Console.WriteLine(item);
}

public class FilterCriterion
{

   public IEnumerable<Occurence> Searches { get; set; }

   public class Occurence
   {
       public string CodeID { get; set; }
       public int? MinOccurences { get; set; }
       public int? MaxOccurences { get; set; }
   }

}

The problem I have is that need to filter the results by the MinOccurences and MaxOccurences filter property and in the end I want the “events” objects where the IDs are 1,2,3 and 4.

Thanks in advance if you can provide help.

Answer 1

To access event.ID at the end of processing you need to pass it with your first query. Alter select to this:

// ...
group e by de into t
select new
{
    PatientID = t.Key.PatientID,
    CodeID = t.Key.CodeID,
    Occurences = t.Count(d => t.Key.CodeID == d.CodeID),
    // taking original items with us
    Items = t
};

Having done that, your final query (including occurrences filter) might look like this:

var result = summary
    // get all necessary data, including filter that matched given item
    .Select(Item => new
        {
            Item,
            Filter = searches.FirstOrDefault(f => f.CodeID == Item.CodeID)
        })
    // get rid of those without matching filter
    .Where(i => i.Filter != null)
    // this is your occurrences filtering
    .Where(i => i.Item.Occurences >= i.Filter.MinOccurences
        && i.Item.Occurences <= i.Filter.MaxOccurences)
    // and finally extract original events IDs
    .SelectMany(i => i.Item.Items)
    .Select(i => i.ID);

This produces 1, 2 as result. 3 and 4 are left out as they don’t get past occurrences filtering.