C# 列表<string>包含特定字符串

Question

I have a list of strings (thing1-3, else1-3, other1-3), and I want to create a simplified list with just (thing, else, other). Seems straight forward (or at least this was with the Classic VB Dictionary .Exists function), but I'm stuck. So I'm checking if the string startswith one of my simplified strings, then if the simplified list does not contain that string, add it. But checking if the simplified list contains the string already is throwing me off.

List<string> myList = new List<string>(new string[] { "thing1", "thing2", "thing3", "else1", "else2", "else3", "other1", "other2", "other3" });

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

foreach (string s in myList)
{
   if (s.StartsWith("thing"))
   {
      if (!myListSimplifed.Contains("thing")) { myListSimplifed.Add("thing"); }
   }

   if (s.StartsWith("else"))
   {
      if (!myListSimplifed.Contains("else")) { myListSimplifed.Add("else"); }
   }

   if (s.StartsWith("other"))
   {
      if (!myListSimplifed.Contains("other")) { myListSimplifed.Add("other"); }
   }
}

I would expect this mySimplifiedList to contain "thing", "else", "other", but it contains thing1-3, else1-2, other1-3.

if (myListSimplified.Exists("thing")) { }

IntelliSense returns "cannot convert from 'string' to 'System.Predicate'

ok.. so this:

if (!myListSimplified.Any(str => str.Contains("thing"))) { myListSimplified.Add("thing"); }

Or

if (!myListSimplified.Exists(str => str.Contains("thing"))) { myListSimplified.Add("thing"); }

None of these work.

Obviously I can create a method to iterate through the list and compare it to a string, but this functionality seems to be too fundamental to lists that MS left it out... Also seems silly to be passing lists around...

private bool Exists(List<string> lList, string sCompare)
{
    bool bVal = false;

    foreach (string s in lList)
    {
        if (s == sCompare) { bVal = true; }
        break;
    }

    return bVal;
}

Answer 1

I'm not sure what your problem is:

First of all, it seems your first code snippet contains a typo: you have List<string> myListSimplified but then inside the foreach you reference myListSimplifed (missing 'i' after the 'f').

If I correct that typo and run your code, then I get a list containing {"thing", "else", "other" } , which seems to be what you also expect.

Answer 2

Besides the typo in myListSimplifed vs myListSimplified your code sample produces what you want it to do.

Not what you ask for, but you can have the same effect with far fewer lines of code:

var myList = new List<string> {"thing1", "thing2", "thing3", "else1", "else2", "else3", "other1", "other2", "other3"};
var myListSimplified = myList.Select(s => new string(s.Where(char.IsLetter).ToArray())).Distinct();

Answer 3

Lists are generic data types. They don't know what strings are, and so they're not provided out of the box with facilities to search for items that StartWith or Contain other strings. This sort of operation doesn't make sense, generically speaking. This is why you have operations like Any that take a lambda function to provide your own logic:

if (myList.Any(str => str.StartsWith("thing")))
     mySimplifiedList.Add("thing");

I've tested this and it works fine.

Of course, if you have multiple strings you want to extract, you should probably make this more generic. The simplest way is to extract the lines above to a method that receives the substring ("thing", in this case) as a parameter. A more generic approach (assuming it matches your data and logic) would be to go over all strings, strip all numerals from it, and store that. Assuming StripNumerals is a method that receives a string, it could look like this, with Distinct ensuring you have only one instance of each string.

var simplifiedList = myList.Select(StripNumerals).Distinct().ToList();

Answer 4

I have noticed your typo when putting the code in Visual Studio. The result is correct, but your algorithm is far from being generic. What you can try:

1. var is useful to simplify declaration
2. list initialization can be simplified

3. obtain a list by stripping all digits and perform a distinct on it

   var myList = new List<string>() { "thing1", "thing2", "thing3", "else1", "else2", "else3", "other1", "other2", "other3" }; var listWithoutNumbers = myList.Select(s => { Regex rgx = new Regex("[0-9]"); return rgx.Replace(s, ""); }); var simplifiedList = listWithoutNumbers.Distinct();

Answer 5

Your original solution works, apart from the typo. However, if you want more generic solution, you could use something like this

List<string> myList = new List<string>(new string[] { "thing1", "thing2", "thing3", "else1", "else2", "else3", "other1", "other2", "other3" });

List<string> myListSimplified = myList.Select(s => new String(s.Where(Char.IsLetter).ToArray())).Distinct().ToList();

Don't forget to add

using System.Linq;

if you will try this solution.