CODEWITHSUNDEEP
c#asp.netcollections
cdub
cdub

Reputation: 25711

C# Collections for Distinct Data

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.

Upvotes: 1

Views: 2999

Answers (3)

Simon
Simon

Reputation: 6152

Perhaps I'm being dense and not fully understanding the question but can't you just use a regular List and just use the .Contains method to check if each string exists in the list before adding it in the loop? You might need to keep an eye on performance if you have a lot of strings.

Upvotes: 0

Tim Schmelter
Tim Schmelter

Reputation: 460138

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

Upvotes: 2

rfmodulator
rfmodulator

Reputation: 3738

If you're using .Net 3.5 or above, put the strings in a List<> and use the linq method Distinct().

using System.Linq;

IEnumerable<string> strs = new List<string>(new[] { "one", "two", "three", "one" });

var distinct = strs.Distinct();

In .Net 2.0 you have no choice but to do it manually.

Upvotes: 1

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