Best way to check for string in comma-delimited list with .NET?

Question

I'm reading a comma-delimited list of strings from a config file. I need to check whether another string is in that list. For example:

"apple,banana,cheese"

If I check for "apple" I should find it, but if I check for "app" I should not.

What's the most straight-forward and concise way to do this? It doesn't have to be fast.

(I'll add my solution as an answer, but I'm hoping someone has something better.)

Answer 1

Regex probably doesn't count as "straight-forward", but this is what I've got:

Regex.IsMatch(listString, "(?<=,|^)" + testWord + "(?=,|$)")

Update: Per Eric's comment below, this should be:

Regex.IsMatch(listString, "(?<=,|^)" + Regex.Escape(testWord) + "(?=,|$)")

Answer 2

(","+listString+",").Contains(","+testWord+",");

but not straight-forward, too.

Answer 3

Using linq:

listString.Split(',').Contains("apple")

W/o linq:

Array.IndexOf(listString.Split(','), "apple") >= 0

Answer 4

Another way might be to try using

bool contains = new List<string>("apple,banana,cheese".Split(',')).Contains("apple");
//or
bool b = "apple,banana,cheese".Split(',').Contains("apple");

List< T>.Contains Method

String.Split Method

Enumerable.Contains Method

Answer 5

Here's an option that ignores case.

var food = "apple,banana,cheese";

bool containsApp = food.Split(',')
                       .Where(s => string.Compare("app", s, true) == 0)
                       .Count() > 0;

bool containsApple = food.Split(',')
                         .Where(s => string.Compare("apple", s, true) == 0)
                         .Count() > 0;

Console.WriteLine("Contains \"app\"? {0}", containsApp);
Console.WriteLine("Contains \"apple\"? {0}", containsApple);

Answer 6

The answer depends on what the syntax rules for your comma-delimited list are.

If the rules require that the list be exactly as you posted (no spaces, no trailing comma) then the task can be broken down into it's component pieces:

Does the string begin with apple,? (String.StartsWith)
Does the string end with ,apple? (String.EndsWith)
Does the string contain ,apple,? (String.Contains)

If the rules are more difficult then the Regex approach becomes the only way without fully processing the list or writing a heap of rules.

If you are checking for many items against the same string you'll want to just transform the string into a list which you cache and then check against. The String.Split method will do this for you.

Answer 7

This works, but regexes are pretty slow if they get complicated. That said, the word boundary anchor makes this sort of thing pretty easy.

var foods = "apple,banana,cheese";

var match = Regex.Match(foods, @"\bapple\b");

if (match.Success)
    Console.WriteLine(match.Value);