C# - combining collections question

Question

If I have a IDictionary<int, int>, is it possible to receive a IEnumerable<int>, which would contain every KeyValuePair<int, int> disassembled into two (int, int) entries inserted one after another?

Small example:

Dictionary:
5 - 25
6 - 36
7 - 49

Wanted Enumerable:
5, 25, 6, 36, 7, 49

Also, I wanted to have this in one super-pretty statement, but I couldn't think of an appropriate one :)

---

Update:

Does LINQ allow to insert more than one element per .Select statement, something sharing the idea of:

xyz.Select(t => (t, null))

so that the resulting Enumerable would contain both t and null right after it?

Answer 1

You could use SelectMany<TSource, TResult>(IEnumerable<TSource>, Func<TSource, IEnumerable<TResult>>) (plus overloads). Here's an example

var dict = new Dictionary<int, int> {
   { 5, 25 },
   { 6, 36 },
   { 7, 49 } 
}; 

var projection = dict.SelectMany(kv => new[] { kv.Key, kv.Value });

As per the comments, this is just one way of achieving what you have asked.

Answer 2

You could create a method that will decompose your dictionary into an IEnumerable in the way you want.

using System.Collections.Generic;
using System;

public class C {

    public static void Main()
    {
        var dic = new Dictionary<int,int>();
        dic[0] = 1;
        dic[2] = 3;
        dic[4] = 5;

        foreach (var i in Decompose(dic))
            Console.WriteLine(i);

        Console.ReadLine();
    }

    public static IEnumerable<int> Decompose(IDictionary<int,int> dic)
    {
        foreach (var i in dic.Keys)
        {
            yield return i;
            yield return dic[i];
        }
    }
}

Output:

  0
  1
  2
  3
  4
  5