>>589
まあそういうのはSelectMany()使うと楽だな

Dictionary<string, List<string>> dsls = new Dictionary<string, List<string>>() {
{ "food", new List<string> { "apple", "onigiri", "melon" } },
{ "drink", new List<string> { "beer", "water" } },
};
var sum = dsls.SelectMany(i => i.Value);
foreach (var s in sum)
Console.WriteLine(s);
Console.WriteLine(sum.Count());// ←これが答えになっている