How to update the value stored in Dictionary in C#?

How to update value for a specific key in a dictionary Dictionary<string, int>?

Solution 1:

Just point to the dictionary at given key and assign a new value:

myDictionary[myKey] = myNewValue;

Solution 2:

It's possible by accessing the key as index

for example:

Dictionary<string, int> dictionary = new Dictionary<string, int>();
dictionary["test"] = 1;
dictionary["test"] += 1;
Console.WriteLine (dictionary["test"]); // will print 2

Solution 3:

You can follow this approach:

void addOrUpdate(Dictionary<int, int> dic, int key, int newValue)
{
    int val;
    if (dic.TryGetValue(key, out val))
    {
        // yay, value exists!
        dic[key] = val + newValue;
    }
    else
    {
        // darn, lets add the value
        dic.Add(key, newValue);
    }
}

The edge you get here is that you check and get the value of corresponding key in just 1 access to the dictionary. If you use ContainsKey to check the existance and update the value using dic[key] = val + newValue; then you are accessing the dictionary twice.

Solution 4:

Use LINQ: Access to dictionary for the key and change the value

Dictionary<string, int> dict = new Dictionary<string, int>();
dict = dict.ToDictionary(kvp => kvp.Key, kvp => kvp.Value + 1);

Solution 5:

Here is a way to update by an index much like foo[x] = 9 where x is a key and 9 is the value

var views = new Dictionary<string, bool>();

foreach (var g in grantMasks)
{
    string m = g.ToString();
    for (int i = 0; i <= m.Length; i++)
    {
        views[views.ElementAt(i).Key] = m[i].Equals('1') ? true : false;
    }
}