Question

i am using a HashSet in order to avoid having two (or more)items with the same value inside my collection , on my work i need to iterate over my hashset and remove its values but unfortunatly i cant do so , what i am trying to do is:

string newValue = "";
HashSet<string> myHashSet;
myHashSet = GetAllValues(); // lets say there is a function which fill the hashset
foreach (string s in myHashSet)
{
       newValue = func(s) // lets say that func on some cases returns s as  it was and
       if(s != newValue)  // for some cases returns another va
       {
             myHashSet.Remove(s);
             myHashSet.Add(newValue);
       }

}

thanks in advance for your kind help

Answer 1

You cannot modify the container while it’s being iterated. The solution would be to project the initial set into a “modified” set using LINQ (Enumerable.Select), and create a new HashSet from the results of the projection.

Since if there is a func with the appropriate signature you can directly stick it into the Enumerable.Select method, and since HashSet has a constructor that accepts an IEnumerable<T>, it all comes down to one line:

var modifiedHashSet = new HashSet(myHashSet.Select(func));