how to change the value of dictionary using linq based on key?

Question

I have a Dictionary which is of type,

  Dictionary<string, string> newdictionary = new Dictionary<string, string>();
  newdictionary.Add("12345", "chip1");
  newdictionary.Add("23456", "chip2");

Now i have a List which is of type

   internal class CustomSerial
    {
        public string SerialNo { get; set; }
        public decimal ecoID { get; set; }
    } 
   var customList = new List<CustomSerial>();
   CustomSerial custObj1= new CustomSerial();
   custObj1.ecoID =1;
   custObj1.SerialNo = "12345";
   customList.Add(custObj1);
   CustomSerial custObj2 = new CustomSerial();
   custObj2.ecoID = 2;
   custObj2.SerialNo = "23456";
   customList.Add(custObj2);

Now i need to update the Initial dictionary by Filtering the Keys with ther SerialNumber and Replacing the values with the ecoID.

When i try this, it gives

  foreach (KeyValuePair<string, string> each in newdictionary)
  {                       
    each.Value = customList.Where(t => t.SerialNo == each.Key).Select(t => t.ecoID).ToString();
  }

System.Collections.Generic.KeyValuePair.Value' cannot be assigned to -- it is read only

Solution 1

LIN(Q) is a tool to query something not to update it. However, you can first query what you need to update. For example:

var toUpdate = customList
   .Where(c => newdictionary.ContainsKey(c.SerialNo))
   .Select(c => new KeyValuePair<string, string>(c.SerialNo, c.ecoID.ToString()));
foreach(var kv in toUpdate)
    newdictionary[kv.Key] = kv.Value;

By the way, you get the "KeyValuePair.Value' cannot be assigned to it is read only" exception because aKeyValuePair<TKey, TValue> is a struct which cannot be modified.

Solution 2

You'd have the simplest in this form: though I don't see why you are assigning the same value but the method applies regardless

 var dictionary = new Dictionary<string, string>() { { "12345", "chip1" }, { "23456", "chip2" } };
                var customList = new List<CustomSerial>() { new CustomSerial() { ecoID = 1, SerialNo = "12345" }, new CustomSerial() { ecoID = 2, SerialNo = "23456" } };

                dictionary.Keys.ToList().ForEach(key =>
                {
                    dictionary[key] = customList.FirstOrDefault(c => c.SerialNo == key).SerialNo;
                });

Comments

[Sajeetharan]

is toUpdate is a dictionary?

[Tim Schmelter]

@Sajeetharan: it's an IEnumerable<KeyValuePair<string, string>>.

[Sajeetharan]

Thanks! will mark it as an answer after testing it :)

[Sajeetharan]

Instead of updating it's adding a new key and value

[Tim Schmelter]

@Sajeetharan: no, i'm first taking only key-values which are already in the dictionary: ...Where(c => newdictionary.ContainsKey(c.SerialNo))

[Sajeetharan]

is it possible for you to tell how can i update the Serialno with the ecoId Having chipids in values

[Tim Schmelter]

@Sajeetharan: i don't understand the question. Do you want to update the key of the dictionary? That's not possible, you need to create a new one.