Search in string list and return as bool

Question

I got a List<string> named Test:

List<string> Test = new List<string>();

I want to add a string to it using Test.Add();, but first I want to check if it already exists in the list.

I thought of something like this:

if (Test.Find("Teststring") != true)
{
   Test.Add("Teststring");
}

However, this returns an error.

do you really want to add duplicate values. – A.T. Nov 26 '13 at 11:52 — A.T., Nov 26 '13 at 11:52
Didn't see that, guess I'm dumb :) – jacobz Nov 26 '13 at 14:54 — jacobz, Nov 26 '13 at 14:54

score 3 · Accepted Answer · edited Dec 09 '13 at 13:25

3

I assume that you if you don't want to add the item if it is already added

Try This:

if (!Test.Contains("Teststring"))
{
   Test.Add("Teststring");
}

edited Dec 09 '13 at 13:25

answered Nov 26 '13 at 11:46

Sudhakar Tillapudi

25,935
5
37
67

3

Don't know who downvoted, but `Contains` is the correct way to check if list contains item – Sergey Berezovskiy Nov 26 '13 at 11:47
He actually wants to add it to the array IF it's already there, for some reason... I'm not the one who downvoted, but that might be why. – Tobberoth Nov 26 '13 at 11:48
1

@Tobberoth ah, I see now. I believe its just wrong attempt to check if item not exist.. Otherwise how OP will add first item? :) – Sergey Berezovskiy Nov 26 '13 at 11:50
1

i think OP wants to add item if its not added. – Sudhakar Tillapudi Nov 26 '13 at 11:51
@lazyberezovsky: yes but if OP wants to add item if it is already added then he can not add it first time itself right? – Sudhakar Tillapudi Nov 26 '13 at 11:54
Yeah, sorry for my mistake. I actually do want to add the item only if it is not there already, guess I'm dumb and didn't check twice – jacobz Nov 26 '13 at 14:57
@2111windows : okay :) hope it helps you – Sudhakar Tillapudi Nov 26 '13 at 14:59

score 2 · Answer 2 · answered Nov 26 '13 at 11:46

Any receives a Predicate. It determines if any element in a collection matches a certain condition. You could do this imperatively, using a loop construct. But the Any extension method provides another way. See this:

bool b1 = Test.Any(item => item == "Teststring");

Also you can use :

if (!Test.Contains("Teststring"))
{
...
    }

score 2 · Answer 3 · edited May 23 '17 at 12:12

If you don't want to add an item twice it is a good indicator that you might use a HashSet<T> instead which is more efficient but doesn't allow duplicates(like a Dictionary with only keys).

HashSet<string> Test = new HashSet<string>();
bool newString = Test.Add("Teststring");

If you need to use the list use List.Contains to check if the string is already in the list.

What is the difference between HashSet and List in C#?

But your code suggests that you only want to add duplicates. I assume that this is not intended.

Ehsan · Answer 4 · 2013-11-26T11:52:00.143

In my opinion you are using the wrong datastructure here. You should use Hashset to avoid duplicates.

The lookup time for Hashset is O(1) whereas for list it is O(n)

The HashSet class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.

This is how your code should look like.

HashSet<string> Test = new HashSet<string>();
Test.Add("Teststring");

score 0 · Answer 5 · answered Nov 26 '13 at 11:47

0

Use Test.Contains("TestString");

answered Nov 26 '13 at 11:47

sh_kamalh

3,853
4
38
50

Search in string list and return as bool

5 Answers5