Question

I have a bunch of string data and I can loop through it one by one. What’s a good collection (and how to implement it) so that I only get the distinct strings?

The client I am doing this for doesn’t even use .NET 3.5 so .Distinct is out. They use .NET framework 2.0.

And I am reading the list one at a time and don’t know how many records it will have until I’m done.

Answer 1

One way is using Distinct to make your strings unique:

List<string> a = new List<string>();
a.AddRange(new string[] { "a", "b", "a", "c", "d", "b" });
List<string> b = new List<string>();
b.AddRange(a.Distinct());

Another resource on LINQ’s Distinct: http://blogs.msdn.com/b/charlie/archive/2006/11/19/linq-farm-group-and-distinct.aspx

Another way: use a HashSet as others suggested;

HashSet<string> hash = new HashSet<string>(inputStrings);

Have a look for this link, to see how to implement it in .net 2.0: https://stackoverflow.com/a/687042/284240

If you’re not on 3.5, you also can do it manually:

List<string> newList = new List<string>();

foreach (string s in list)
{
   if (!newList.Contains(s))
      newList.Add(s);
}
// newList contains the unique values

Another solution (maybe a little faster):

Dictionary<string,bool> dic = new Dictionary<string,bool>();

foreach (string s in list)
{
   dic[s] = true;
}

List<string> newList = new List<string>(dic.Keys);
// newList contains the unique values

https://stackoverflow.com/a/1205813/284240