Using LINQ, find the minimum value of an item property, in a collection, in a dictionary

Question

public class Item
{
  public double findMe{ get; set; } 
  public int? iMayBeNull { get; set; }
}

public Dictionary<int, ICollection<Item>> TheDictionary{ get; set; }

...

TheDictionary dict = new Dictionary<int, ICollection<Item>>();

I'm trying to find the minimum value of "findMe" where "iMayBeNull" is null in all of "dict"'s collections.

I can't seem to wrap my head around this one.

Any guidance would be greatly appreciated.

Answer 1

Use .SelectMany to coalesce all the collections into one big sequence, then just use the standard .Where and .Min operators:

TheDictionary.Values
    .SelectMany(x => x)
    .Where(x => x.iMayBeNull == null)
    .Min(x => x.findMe);

Answer 2

The LINQ expression parallel to the SelectMany method is the multiple from clause.

Example:

var seq = from col in dict.Values
            from item in col
            where item.iMayBeNull == null
            select item.findMe;

var min = seq.Min();