Check array for string that starts with given one (ignoring case)

Question

I am trying to see if my string starts with a string in an array of strings I've created. Here is my code:

string x = "Table a";
string y = "a table";
string[] arr = new string["table", "chair", "plate"]
if (arr.Contains(x.ToLower())){
    // this should be true
 }
if (arr.Contains(y.ToLower())){
    // this should be false
 }

How can I make it so my if statement comes up true? Id like to just match the beginning of string x to the contents of the array while ignoring the case and the following characters. I thought I needed regex to do this but I could be mistaken. I'm a bit of a newbie with regex.

Answer 1

It seems you want to check if your string contains an element from your list, so this should be what you are looking for:

if (arr.Any(c => x.ToLower().Contains(c)))

Or simpler:

if (arr.Any(x.ToLower().Contains))

Or based on your comments you may use this:

if (arr.Any(x.ToLower().Split(' ')[0].Contains))

Answer 2

Because you said you want regex...
you can set a regex to var regex = new Regex("(table|plate|fork)");
and check for if(regex.IsMatch(myString)) { ... }

but it for the issue at hand, you dont have to use Regex, as you are searching for an exact substring... you can use
(as @S.Akbari mentioned : if (arr.Any(c => x.ToLower().Contains(c))) { ... }

Answer 3

Enumerable.Contains matches exact values (and there is no build in compare that checks for "starts with"), you need Any that takes predicate that takes each array element as parameter and perform the check. So first step is you want "contains" to be other way around - given string to contain element from array like:

   var myString = "some string"
   if (arr.Any(arrayItem => myString.Contains(arrayItem)))...

Now you actually asking for "string starts with given word" and not just contains - so you obviously need StartsWith (which conveniently allows to specify case sensitivity unlike Contains - Case insensitive 'Contains(string)'):

      if (arr.Any(arrayItem => myString.StartsWith(
               arrayItem, StringComparison.CurrentCultureIgnoreCase))) ...

Note that this code will accept "tableAAA bob" - if you really need to break on word boundary regular expression may be better choice. Building regular expressions dynamically is trivial as long as you properly escape all the values.

Regex should be

• beginning of string - ^
• properly escaped word you are searching for - Escape Special Character in Regex

• word break - \b

    if (arr.Any(arrayItem => Regex.Match(myString,
          String.Format(@"^{0}\b", Regex.Escape(arrayItem)), 
          RegexOptions.IgnoreCase)) ...
  

Answer 4

you can do something like below using TypeScript. Instead of Starts with you can also use contains or equals etc..

  public namesList: Array<string> = ['name1','name2','name3','name4','name5'];

// SomeString = 'name1, Hello there';
      private isNamePresent(SomeString : string):boolean{
        if (this.namesList.find(name => SomeString.startsWith(name)))
          return true;
        return false;
      }

Answer 5

I think I understand what you are trying to say here, although there are still some ambiguity. Are you trying to see if 1 word in your String (which is a sentence) exists in your array?

@Amy is correct, this might not have to do with Regex at all.

I think this segment of code will do what you want in Java (which can easily be translated to C#):

Java:

x = x.ToLower();
string[] words = x.Split("\\s+");
foreach(string word in words){
    foreach(string element in arr){
        if(element.Equals(word)){
            return true;
        }
    }
} 
return false;

You can also use a Set to store the elements in your array, which can make look up more efficient.

Java:

x = x.ToLower();
string[] words = x.Split("\\s+");
HashSet<string> set = new HashSet<string>(arr);
for(string word : words){
    if(set.contains(word)){
        return true;
    }
} 
return false;

Edit: (12/22, 11:05am)

I rewrote my solution in C#, thanks to reminders by @Amy and @JohnyL. Since the author only wants to match the first word of the string, this edited code should work :)

C#:

    static bool contains(){
        x = x.ToLower();
        string[] words = x.Split(" ");
        var set = new HashSet<string>(arr);
        if(set.Contains(words[0])){
            return true;
        }
        return false;
    }

Answer 6

Sorry my question was so vague but here is the solution thanks to some help from a few people that answered.

var regex = new Regex("^(table|chair|plate) *.*");
if (regex.IsMatch(x.ToLower())){}