Question

I have following two approaches. Approach 1 uses a HashSet and List. Second approach uses Sorting of Array.

Which is better in terms of processing speed

1. when there are many records?
2. when there is small number of records?

CODE

        string entryValue = "A,B, a , b, ";

        if (!String.IsNullOrEmpty(entryValue.Trim()))
        {

            //APPROACH 1
            bool isUnique = true;

            //Hash set is unique set  -- Case sensitivty Ignored
            HashSet<string> uniqueRecipientsSet = new HashSet<string>(entryValue.Trim().Split(',').Select(t => t.Trim()),StringComparer.OrdinalIgnoreCase );

            //List can hold duplicates
            List<string> completeItems = new List<string>(entryValue.Trim().Split(',').Select(t => t.Trim()));

            if (completeItems.Count != uniqueRecipientsSet.Count)
            {
                isUnique = false;
            }


            //APPROACH 2
            bool isUniqueCheck2 = true;
            string[] words = entryValue.Split(',');
            Array.Sort(words);

            for (int i = 1; i < words.Length; i++)
            {
                if (words[i].ToLower().Trim() == words[i - 1].ToLower().Trim())
                {
                    isUniqueCheck2 = false;
                    break;
                }
            }


            bool result1 = isUnique;
            bool result2 = isUniqueCheck2;


        }

REFERENCES:

1. Split comma separated string to count duplicates
2. MSDN Blog – Find Duplicates using LINQ

Answer 1

You can simplify your first approach:

List<string> completeItems = new List<string>(entryValue.Trim().Split(',').Select(t => t.Trim()));
isUnique = completeItems.Count == completeItems.Distinct().Count();

This would eliminate multiple splitting, and hide the hash set behind the call of Distinct(). Note that the if statement is also unnecessary.