How to add duplicate keys into the Dictionary

Question

I have some lines from text files that i want to add into the Dictionary.I am using Dictionary for the first time.While adding up starting lines it was Ok but suddenly i got err

Answer 1

how to allow to add duplicate keys in Dictionary

It is not possible. All keys should be unique. As Dictionary<TKey, TValue> implemented:

Every key in aDictionary<TKey, TValue> must be unique according to the dictionary's equality comparer.

Possible solutions - you can keep collection of strings as value (i.e. use Dictionary<string, List<string>>), or (better) you can use Lookup<TKey, TValue> instead of dictionary.

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how to check for duplicate keys and delete previous value from Dictionary?

You can check if the key exists with previousLines.ContainsKey(dialedno) but if you always want to hold the last line, then just replace whatever dictionary had for the key, or add the new key if it is not in the dictionary:

previousLines[dialedno] = line;

Answer 2

Its not possible to add duplicate items to a Dictionary - an alternative is to use the Lookup class.

Enumerable.ToLookup Method

Creates a generic Lookup from an IEnumerable.

Answer 3

List< KeyValuePair < string, string>> listKeyValPair= new List< KeyValuePair< string, string>>();
KeyValuePair< string, string> keyValue= new KeyValuePair< string, string>("KEY1", "VALUE1");
listKeyValPair.Add(keyValue);

Answer 4

Example:

class Program
        {
             private static List<KeyValuePair<string, int>> d = new List<KeyValuePair<string, int>>();

            static void Main(string[] args)
            {
                 d.Add(new KeyValuePair<string, int>("joe", 100));
                 d.Add(new KeyValuePair<string, int>("joe", 200));
                 d.Add(new KeyValuePair<string, int>("jim", 100));
                 var result = d.Where(x => x.Key == "joe");
                foreach(var q in result)
                    Console.WriteLine(q.Value   );
                Console.ReadLine();
            }
         }

Answer 5

We can Use a List of Key Value Pair

List<KeyValuePair<string, string>> myduplicateLovingDictionary= new List<KeyValuePair<string, string>>();
KeyValuePair<string,string> myItem = new KeyValuePair<string,string>(dialedno, line);
myduplicateLovingDictionary.Add(myItem);

Answer 6

If your question is if you can add the same key twice, the answer is No. However if you want to just iterate through the item and then increase the count of the value for the particular Key, you can achieve that by using "TryAdd" method.

var dict = new Dictionary<int, int>();
        foreach (var item in array)
        {
            dict.TryAdd(item, 0);
            dict[item]++;
        }

The same thing we are trying to achieve with if else, can be achieved with this method.``

https://docs.microsoft.com/en-us/dotnet/api/system.collections.concurrent.concurrentdictionary-2.tryadd?view=netframework-4.7.2