Case-Insensitive List Search

user_458213 0
Viewed 172717

I have a list testList that contains a bunch of strings. I would like to add a new string into the testList only if it doesn't already exist in the list. Therefore, I need to do a case-insensitive search of the list and make it efficient. I can't use Contains because that doesn't take into account the casing. I also don't want to use ToUpper/ToLower for performance reasons. I came across this method, which works:

    if(testList.FindAll(x => x.IndexOf(keyword, 
                       StringComparison.OrdinalIgnoreCase) >= 0).Count > 0)
       Console.WriteLine("Found in list");

This works, but it also matches partial words. If the list contains "goat", I can't add "oat" because it claims that "oat" is already in the list. Is there a way to efficiently search lists in a case insensitive manner, where words have to match exactly? thanks

case-insensitive list search c#
8 Answers

You can use StringComparer static variants with the Contains overload from LINQ for example, like this:

using System.Linq;

var list = new List<string>();
list.Add("cat");
list.Add("dog");
list.Add("moth");

if (list.Contains("MOTH", StringComparer.OrdinalIgnoreCase))
{
    Console.WriteLine("found");
}
user_28247910

Below is the example of searching for a keyword in the whole list and remove that item:

public class Book
{
  public int BookId { get; set; }
  public DateTime CreatedDate { get; set; }
  public string Text { get; set; }
  public string Autor { get; set; }
  public string Source { get; set; }
}

If you want to remove a book that contains some keyword in the Text property, you can create a list of keywords and remove it from list of books:

List<Book> listToSearch = new List<Book>()
   {
        new Book(){
            BookId = 1,
            CreatedDate = new DateTime(2014, 5, 27),
            Text = " test voprivreda...",
            Autor = "abc",
            Source = "SSSS"

        },
        new Book(){
            BookId = 2,
            CreatedDate = new DateTime(2014, 5, 27),
            Text = "here you go...",
            Autor = "bcd",
            Source = "SSSS"


        }
    };

var blackList = new List<string>()
            {
                "test", "b"
            }; 

foreach (var itemtoremove in blackList)
    {
        listToSearch.RemoveAll(p => p.Source.ToLower().Contains(itemtoremove.ToLower()) || p.Source.ToLower().Contains(itemtoremove.ToLower()));
    }


return listToSearch.ToList();
user_46548460
Related