Merge two list with some conditional

Actually you are finding element from root means using // in your xpath which will search for elements in the whole page while you need to search within the specific row element only so you should try with .// in your xpath which will search for elements only specific element context. So I think you should try as below which will gives you only desire elements list instead of large amount of elements list as below :

ReadOnlyCollection<IWebElement> lstTable = browser.FindElements(By.XPath("//table/tbody/tr"));foreach (IWebElement val in lstTable){  ReadOnlyCollection<IWebElement> lstSpecialEle = val.FindElements(By.XPath(".//td/span | .//td/b | .//td/p"));}

Edited1 : If your getting list of elements with the combination of null text you can filter it with null condition and get sublists which contains exact text as below :-

var FinalList = lstSpecialEle.Where(x=>x.Text != null).ToList();

Edited2 :- if you want to merge all columns text list into Single list of string try as below :-

List<string> FinalList = new List <string>();foreach (IWebElement val in lstTable){    ReadOnlyCollection<IWebElement> lstSpecialEle = val.FindElements(By.XPath(".//td/span | .//td/b | .//td/p"));    var AllTextList = lstSpecialEle.Where(x=>x.Text != null).ToList().Select(El => El.Text).ToList();     string AllText = String.Join(" ", AllTextList);     FinalList.Add(AllText);       }Console.WriteLine(FinalList);

Now FinalList will contain all values separated by per row.

Hope it helps...:)