Update Dictionary Value field through loop

Question

I have defined a Dictionary as follows:

Dictionary<string, double> collection = new Dictionary<string, double>();

Now i want to update my Value:

foreach (KeyValuePair<string, double> pair int collection)
{
    double val = 3.0;
    collection[pair.Value] = val; // Get an error
}

My error is Cannot convert from double to string. Why is that ?

that won't compile `int` should be `in` – fubo Oct 01 '15 at 11:17 — fubo, Oct 01 '15 at 11:17

score 2 · Accepted Answer · answered Oct 01 '15 at 11:33

You can't iterate over a Dictionary and change the internal value as it will break the iterator.

you need to copy the collection, and modify the copied version...example below:

Dictionary<string, double> collection = new Dictionary<string, double>();
collection.Add("A", 1.0);
collection.Add("B", 2.0);

Dictionary<string, double> collection2 = new Dictionary<string, double>(collection);

foreach (KeyValuePair<string, double> pair in collection)
{
  double val = 3.0;              
  collection2.Remove(pair.Key);
  collection2.Add(pair.Key, val);
 }

Arash · Answer 2 · 2015-10-01T11:37:35.200

0

Try this

   Dictionary<string, double> Copycollection= new Dictionary<string, double>  (collections);
            foreach (KeyValuePair<string, double> pair in Copycollection)
             {
                double val = 3.0;
                collection[pair.Key] = val; 
            }

edited Oct 01 '15 at 11:37

answered Oct 01 '15 at 11:18

Arash

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1

This won't work as you are not allowed to change collection during enumerating. See [related](http://stackoverflow.com/q/2260446/1997232) question. – Sinatr Oct 01 '15 at 11:25

Update Dictionary Value field through loop

2 Answers2