How to merge two dictionaries in C# with duplicates - c#-3.0

Question

Is there a way in C# to merge two dictionaries? I have two dictionaries that may has the same keys, but I am looking for a way to merge them so, in the end there is a dictionary with one key and the values from both the dictionaries merged.
I found the following code but it does not handle duplicates.
Dictionary Mydictionary<string, string[]> = new Dictionary<string, string[]>();
Mydictonary.Union(secondDictionary).ToDictionary( pair => pair.Key, pair => pair.Value);

Answer 1

If you want a LINQ approach, try this:
Dictionary<string, string[]> firstDic = new Dictionary<string, string[]>
{
{"apple", new [] {"red"}},
{"orange", new [] {"orange"}}
};
Dictionary<string, string[]> secondDic = new Dictionary<string, string[]>
{
{"apple", new [] {"green"}},
{"banana", new [] {"yellow"}}
};
Dictionary<string, string[]> resultDic = firstDic.Union(secondDic)
.GroupBy(o => o.Key)
.ToDictionary(o => o.Key, o => o.SelectMany(kvp => kvp.Value).ToArray());
For the sample data, you'll get a Dictionary with 3 KeyValuePairs, and the item with a Key of "apple" will have an Array with "red" and "green" for the value.

Answer 2

Maybe something like this:
foreach (var value in secondDictionary)
if (myDictionary.Contains(value.Key))
myDictionary[value.Key] = myDictionary[value.Key]
.Concat(value.Value).ToArray();
else
myDictionary[value.Key] = value.Value;

Answer 3

This should do it:
Dictionary<string, string[]> dict1 = new Dictionary<string, string[]>();
Dictionary<string, string[]> dict2 = new Dictionary<string, string[]>();
Dictionary<string, List<string>> combined = new Dictionary<string, List<string>>();
foreach (var pair in dict1) combined.Add(pair.Key, new List<string>(pair.Value));
foreach (var pair in dict2)
{
List<string> list;
if (!combined.TryGetValue(pair.Key, out list)) combined.Add(pair.Key, list = new List<string>());
list.AddRange(pair.Value);
}
If you really want the result as a Dictionary<string, string[]>, you can tack this on to the end:
Dictionary<string, string[]> combinedArray = new Dictionary<string, string[]>();
foreach (var pair in combined) combinedArray.Add(pair.Key, pair.Value.ToArray());