Clever Geek Handbook

Substrings, search lists

I have a list that is populated with user-entered strings. I have already verified that the string is not empty and that the list does not contain that string.

The problem I ran into was to check if the user entered string was a string from a string in a list.

List<string> stringlist = new List<string>();
int index = 0;
string userinput = null;

while (userinput != "end")
{
    userinput = getstring();
    if (stringlist.Contains(userinput))
    {
        Console.WriteLine(" Term has been stored previously.");
    }
    else
    {
        stringlist.Insert(index, userinput);
        index += 1;
    }

    foreach (string s in stringlist)
    {
        Console.WriteLine("List contains : {0}", s);
        if (s.Contains(userinput))
        {
            // something?
        }
    }
} // end of main while loop

So, in principle, if the term someone introduces is "dog", if one of the other strings entered is "bigdog", it should say "dog is a substring of bigdog" or something similar. Should I use a different loop type for this?

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5 answers


To summarize each tip:

  • Check substrings before adding an entry to the list
  • Use a method String.Contains()

    to check a substring for each item in a list

  • Use a method List.Add

    and then use memory in a variableindex 

    List<string> stringlist = new List<string>();
string userinput = null;

while (userinput != "end")
{
userinput = getstring();

// Check for Substrings
foreach (string s in stringlist.Where(s => s.Contains(userinput)))
{
    Console.WriteLine("{0} is a substring of {1}", userinput, s);
}

// Add to the list
if (stringlist.Contains(userinput))
{
    Console.WriteLine(" Term has been stored previously.");
}
else
{
    stringlist.Add(userinput);
}
} // end of main while loop


You can use the Regex

(Regular Expressions) class to find matches in a list, but it still requires a loop foreach

, and String.Contains

will actually outperform for simple substring searches Regex.IsMatch

. I also tried to concatenate a long string list and search there in the same line of code, but this is highly susceptible to false positives as some individual entries can create new words when concatenated.

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foreach (string s in stringlist)
{
    if (s.Contains(userinput))
    {
        Console.WriteLine("{0} is a substring of {1}", userinput, s);
    }
}


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stringlist.ForEach(s =>
 {
   if (s.Contains(userinput))
   {
       Console.WriteLine("{0} is a substring of {1}", userinput, s);
   }
 });
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More streamlined way.

   foreach (string s in stringlist.Where(s => s.Contains(userinput)))
          {
              Console.WriteLine("{0} is a substring of {1}", userinput, s);
          }
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stringlist.Where(s => s.Contains(userinput) || userinput.Contains(s)).ToList().ForEach(s => Console.WriteLine("Part of {0} is a substring of {1}", userinput, s));

You can use ToLower()

it if you want it to be case insensitive.

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