C# appending Dictionary

Question

how can i append Dictionary into another Dictionary ?

Dictionary<string, DateTime> odict = new Dictionary<string, DateTime>();
        //Liste tous les Clients EMAIL (3)
        foreach (var TheClientID in TheClient.GetClient_Id(3))
        {
            Dictionary<string, DateTime> Temp = oEmail.VoirEML(TheClientID.Key);
             //odict = odict.Concat(Temp).ToDictionary(pair => pair.Key, pair => pair.Value);
            odict = odict.SelectMany(toto => Temp)
                     .ToLookup(pair => pair.Key, pair => pair.Value)
                     .ToDictionary(group => group.Key, group => group.First());
        }

i want to concat / append dictionary without double the entry.

Answer 1

I once wrote an extension method for that because I needed the same. The last parameter decides what to do when duplicate keys are encountered.

Skip means source entry is kept.

Overwrite means "other" entry is used.

Throw will throw an Exception.

public enum DuplicateKeyHandling
{
    Skip,
    Overwrite,
    Throw
}

/// <summary>
/// Combines two dictionaries into one dictionary. The contents of the resulting dictionary depends on the <paramref name="duplicateKeyHandling"/> parameter.
/// </summary>
/// <typeparam name="TKey">The type of the keys in the dictionaries</typeparam>
/// <typeparam name="TValue">The type of the values in the dictionaries</typeparam>
/// <param name="this"></param>
/// <param name="other">The dictionary to combine this one with</param>
/// <param name="duplicateKeyHandling">Specifies how to react if the <paramref name="other"/> dictionary contains keys that are already in this dictionary</param>
/// <returns>A new dictionary containing the combined key-value-pairs of both source dictionaries</returns>
public static Dictionary<TKey, TValue> Combine<TKey, TValue>(this Dictionary<TKey, TValue> @this, Dictionary<TKey, TValue> other, DuplicateKeyHandling duplicateKeyHandling = DuplicateKeyHandling.Skip)
{
    // EDIT: I added the "comparer" parameter so the resulting dictionary will
    // use the same comparer as the first source dictionary
    var result = new Dictionary<TKey, TValue>(@this, @this.Comparer);

    foreach (KeyValuePair<TKey, TValue> kvp in other)
    {
        if (result.ContainsKey(kvp.Key))
        {
            if (duplicateKeyHandling == DuplicateKeyHandling.Overwrite)
            {
                result[kvp.Key] = kvp.Value;
            }

            if (duplicateKeyHandling == DuplicateKeyHandling.Throw)
            {
                throw new Exception("Duplicate key while combining dictionaries!");
            }
        }
        else
        {
            result.Add(kvp.Key, kvp.Value);
        }
    }

    return result;
}

Answer 2

I think trying to use Linq is a mistake. It is easy to write and easy to read with a simple loop, and the extensions methods will not be any more efficient -- probably less efficient.

    Dictionary<string, DateTime> odict = new Dictionary<string, DateTime>();
    //Liste tous les Clients EMAIL (3)
    foreach(var TheClientID in TheClient.GetClient_Id(3)) {
            Dictionary<string, DateTime> Temp = oEmail.VoirEML(TheClientID.Key);
            //odict = odict.Concat(Temp).ToDictionary(pair => pair.Key, pair => pair.Value);
            foreach(var kvp in Temp){
                    odict[kvp.Key] = kvp.Value;
        }
    }

Answer 3

i try this :

odict = odict.Concat(Temp.Where(kvp => !odict.ContainsKey(kvp.Key))).ToDictionary(x => x.Key, x => x.Value);

and it works fine