In C#, best way to check if stringbuilder contains a substring

Question

I have an existing StringBuilder object, the code appends some values and a delimiter to it. Now I want to modify the code to add the logic that before appending the text I want to check if it really exist in string builder variable or not? If not, then only append otherwise ignore. What is the best way to do so? Do I need to change the object to string type? Need a best approach that would not hamper a performance.

public static string BuildUniqueIDList(context RequestContext)
{
    string rtnvalue = string.Empty;
    try
    {
        StringBuilder strUIDList = new StringBuilder(100);
        for (int iCntr = 0; iCntr < RequestContext.accounts.Length; iCntr++)
        {
            if (iCntr > 0)
            {
                strUIDList.Append(",");
            }
            //need to do somthing like strUIDList.Contains(RequestContext.accounts[iCntr].uniqueid) then continue other wise append
            strUIDList.Append(RequestContext.accounts[iCntr].uniqueid);
        }
        rtnvalue = strUIDList.ToString();
    }
    catch (Exception e)
    {
        throw;
    }
    return rtnvalue;
}

I am not sure if having something like will be efficient: if (!strUIDList.ToString().Contains(RequestContext.accounts[iCntr].uniqueid.ToString()))

Answer 1

Personally I would use:

return string.Join(",", RequestContext.accounts
                                      .Select(x => x.uniqueid)
                                      .Distinct());

No need to loop explicitly, manually use a StringBuilder etc... just express it all declaratively :)

(You'd need to call ToArray() at the end if you're not using .NET 4, which would obviously reduce the efficiency somewhat... but I doubt it'll become a bottleneck for your app.)

EDIT: Okay, for a non-LINQ solution... if the size is reasonably small I'd just for for:

// First create a list of unique elements
List<string> ids = new List<string>();
foreach (var account in RequestContext.accounts)
{
    string id = account.uniqueid;
    if (ids.Contains(id))
    {
        ids.Add(id);
    }
}

// Then convert it into a string.
// You could use string.Join(",", ids.ToArray()) here instead.
StringBuilder builder = new StringBuilder();
foreach (string id in ids)
{
    builder.Append(id);
    builder.Append(",");
}
if (builder.Length > 0)
{
    builder.Length--; // Chop off the trailing comma
}
return builder.ToString();

If you could have a large collection of strings, you might use Dictionary<string, string> as a sort of fake HashSet<string>.