I can't figure out how to keep the keys and values on a dictionary when I try to merge two dictionaries. I keep getting ArgumentException due to duplicate of key. When the key match I would just like to add the value by = kvp.value;

I have a list of Dictionaries where the

1st Dictionary = kvp = "jump", 2;

2ndDictionary = kvp = "jump", 4;

I like to merge them and get something like: Dictionary = kvp = "jump", 6;

That I can later add to my list of Dictionaries

I've tried to run something I found in StackOverflow thread.

foreach (var dict in listOfDict)
{
         dict.SelectMany(d => d)
            .ToLookup(pair => pair.Key, pair => pair.Value)
            .ToDictionary(group => group.Key, group => group.First());
}

But I keep getting.

cannot be inferred from the usage. Try specifying the type arguments explicitly.

I want to avoid getting all keys and all values on separate lists that I later loop through to add key and value on a new dictionary.

CodePudding user response：

If you like the LINQ approach, I would go with something like this:

    var dictionaries = new List<Dictionary<string, int>>(); // this is the list of dictionaries you want to merge
    var unifiedDictionary = new Dictionary<string, int>(); // this is the dictionary where you merge and add the values

    foreach (var kvp in dictionaries.SelectMany(dictionary => dictionary))
    {
        if (unifiedDictionary.ContainsKey(kvp.Key))
        {
            unifiedDictionary[kvp.Key]  = kvp.Value;
        }
        else
        {
            unifiedDictionary.Add(kvp.Key, kvp.Value);
        }
    }

However, if this is too hard to read (I am not always a fan of excessive LINQ over explicit code blocks), you can use the for-loop approach:

    var dictionaries = new List<Dictionary<string, int>>(); // this is the list of dictionaries you want to merge
    var unifiedDictionary = new Dictionary<string, int>(); // this is the dictionary where you merge and add the values

    foreach (var dictionary in dictionaries)
    {
        foreach (var kvp in dictionary)
        {
            if (unifiedDictionary.ContainsKey(kvp.Key))
            {
                unifiedDictionary[kvp.Key]  = kvp.Value;
            }
            else
            {
                unifiedDictionary.Add(kvp.Key, kvp.Value);
            }
        }
    }

Hope this helps you. If further help and explanations are needed, please tell me.

CodePudding user response：

Simplest extension to list of dictionary of double values with using Linq:

public static class ExtListOfDict {
    public static Dictionary<TKey, double> SumValue1<TKey>(this List<Dictionary<TKey, double>> list)        
        => list?.SelectMany(i => i).ToLookup(i => i.Key, i => i.Value).ToDictionary(i => i.Key, i => i.Sum());

}

without linq:

public static Dictionary<TKey, double> SumValue2<TKey>(this List<Dictionary<TKey, double>> list) {
    if(list?.Count > 0) {
        var dir = new Dictionary<TKey, double>(list[0]);
        for(var i = 1; i < list.Count; i  ) 
            foreach (var kv in list[i])
                if (dir.TryGetValue(kv.Key, out double sum))
                    dir[kv.Key] = sum   kv.Value; 
                else 
                    dir.Add(kv.Key, kv.Value);                    
        return dir;
    } else
        return null;
}

CodePudding user response：

If you are getting an exception due to duplicate keys, then it sounds like you have duplicate keys!

Have you checked the two dictionaries before you try to merge them? Simply calling = kvp.value without checking to see if the first dictionary already has a key of that name is very likely to be your problem.

You need to check for an existing entry with that key, and if one is found, take whatever action is appropriate for your scenario (ie ignore, overwrite, ask the user to decide, etc)

CodePudding user response：

Here is a solution based on the CollectionsMarshal.GetValueRefOrAddDefault API (.NET 6), and on the INumber<TSelf> interface (.NET 7):

public static Dictionary<TKey, TValue> ToSumDictionary<TKey, TValue>(
    this IEnumerable<Dictionary<TKey, TValue>> dictionaries)
    where TValue : struct, INumber<TValue>
{
    ArgumentNullException.ThrowIfNull(dictionaries);
    Dictionary<TKey, TValue> result = null;
    foreach (var dictionary in dictionaries)
    {
        if (result is null)
        {
            result = new(dictionary, dictionary.Comparer);
            continue;
        }
        if (!ReferenceEquals(dictionary.Comparer, result.Comparer))
            throw new InvalidOperationException("Incompatible comparers.");
        foreach (var (key, value) in dictionary)
        {
            ref TValue refValue = ref CollectionsMarshal
                .GetValueRefOrAddDefault(result, key, out bool exists);
            refValue = exists ? refValue   value : value;
        }
    }
    result ??= new();
    return result;
}

The key of each KeyValuePair<TKey, TValue> in each dictionary is hashed only once.