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How to combine two dictionaries in C # with duplicates

Is there a way in C # to combine two dictionaries? I have two dictionaries that may have the same keys, but I'm looking for a way to merge them, so at the end there is a dictionary with the same key and values ​​from both dictionaries. I found the following code, but it doesn't handle duplicates.

Dictionary Mydictionary<string, string[]> = new Dictionary<string, string[]>();
Mydictonary.Union(secondDictionary).ToDictionary( pair => pair.Key, pair => pair.Value);
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3 answers


If you need 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 this example, you will get a dictionary with 3 KeyValuePairs, and the item with key "apple" will have an array with "red" and "green" for the value.

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Perhaps 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;
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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 to get the result like Dictionary<string, string[]>

, you can do it all the way:

Dictionary<string, string[]> combinedArray = new Dictionary<string, string[]>();

foreach (var pair in combined) combinedArray.Add(pair.Key, pair.Value.ToArray());
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