how to take dictionary's top N values in c# by linq?

Question

Dictionary<string,List<string>> dict =new Dictionary<string,List<string>>(){...};

I need a result of dictionary type that filtered by LINQ; the filter condition is: if TValue's count > CONST_MAX, then TValue only return top CONST_MAX items .

Answer 1

Dictionary<TKey, TValue> doesn't maintain order. You might want to use SortedDictionary<TKey, TValue> for getting top x items.

Answer 2

Since your question is unclear, I'm going to assume you're looking for a new dictionary with the same keys, but only the first N items in each value:

var firstN = dict.ToDictionary(
                  kvp => kvp.Key,
                  kvp => kvp.Value.Take(CONST_MAX).ToList());

Answer 3

try : if you are comparing value of dic

return mydic
    .Where(p => p.value == myvalue)
    .ToDictionary(p => p.Key, p => p.Value);

Answer 4

Use the Take() method

       Dictionary<string, string> colours = new Dictionary<string, string>();

        colours.Add("1", "Red");
        colours.Add("2", "Black");
        colours.Add("3", "Green");
        colours.Add("4", "Yellow");

        var top2 = colours.Take(2);

        foreach (KeyValuePair<string, string> colour in top2)
        {
            Console.WriteLine("{0}-{1}", colour.Key, colour.Value);
        }