C＃不同的逗号分隔值不起作用

Question

I am trying to remove duplicate values from a comma-separated string, and am having inconsistent results. For example,

If I pass:

STA27,STA27,STA27B,STA27A,STA27B,

I get:

STA27,STA27,STA27B,STA27A,

Or, if I pass:

STA24,STA24,STA24,STA24,

I get:

STA24,STA24,

I've tried several ways to get rid of the comma on the end, but nothing seems to work. I don't understand why Distinct isn't working either. I thought it had something to do with the way the string is terminated, but in the first example I'm getting duplicates of the first two entries, so it doesn't seem to be a position issue.

Any thoughts?

 public string FindDistinctBeats(String Beats)
    // Accept comma-separated string, return distinct values
    {
        string result = string.Empty;

        try
        {
            result = string.Join(",", Beats.Split(',').Distinct().ToArray());
            result = result.TrimEnd(',');

            if (String.IsNullOrEmpty(result))
            {
                return result;
            }
            else
            {
                return result.TrimEnd(result[result.Length - 1]);
            }

        }
        catch (Exception e)
        {
            return e.ToString();
        }
    }

Answer 1

A simple test shows the expected results:

public class Distinct
{
    private string input = "STA27,STA27,STA27B,STA27A,STA27B,";

    [Test]
    public void DistinctTest()
    {
        var distincts = input.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries).Distinct();
        foreach(var entry in distincts)
        {
            Console.WriteLine(entry);
        }
    }
}

Output

STA27
STA27B
STA27A

Answer 2

You were missing the StringSplitOptions.RemoveEmptyEntries options, as already mentioned. Also, consider cleaning up your string before doing the split, something like this:

// test string with some whitespace and a control char in the end of the string
string beats = "STA27,STA27,STA27B,STA27A,STA27B,   " + '\u0002'; 

beats = string.Join(string.Empty, beats.ToCharArray().Where(x => !Char.IsControl(x) && !Char.IsWhiteSpace(x)));

List<string> distinctBeats = beats.Split(",", StringSplitOptions.RemoveEmptyEntries)
                                  .Distinct()
                                  .ToList();

And in case you need a case-insensitive distinct, you can use a StringComparer (in this case, StringComparer.InvariantCultureIgnoreCase ):

List<string> distinctBeats = beats.Split(",", StringSplitOptions.RemoveEmptyEntries)
                                  .Distinct(StringComparer.InvariantCultureIgnoreCase)
                                  .ToList();

Answer 3

Many answers have the proper guidance, but I want to point out that the original code had 2 issues. However, the code as written above run with the input provided does not return the output you specified. I created a fiddler below to show that.

One is the return result.TrimEnd(result[result.Length - 1]); which knocks off that last character of the result. With that if statement removed, the code works fine.

The other is the trailing comma. While you are handling with removing the trailing comma explicitly, you can also use StringSplitOptions.RemoveEmptyEntries . The trailing space causes string.Empty to be the last result in your split.

Here's an example program, and here is a link to a fiddler to run it:

using System;
using System.Linq;

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Original:");
        Console.WriteLine(OriginalFindDistinctBeats("STA24,STA24,STA24,STA24,"));
        Console.WriteLine(OriginalFindDistinctBeats("STA27,STA27,STA27B,STA27A,STA27B,"));

        Console.WriteLine();

        Console.WriteLine("New working (removed that weird if statement):");
        Console.WriteLine(NewFindDistinctBeats("STA24,STA24,STA24,STA24,"));
        Console.WriteLine(NewFindDistinctBeats("STA27,STA27,STA27B,STA27A,STA27B,"));

        Console.WriteLine();

        Console.WriteLine("New working with remove empty:");
        Console.WriteLine(NewWithRemoveEmptyFindDistinctBeats("STA24,STA24,STA24,STA24,"));
        Console.WriteLine(NewWithRemoveEmptyFindDistinctBeats("STA27,STA27,STA27B,STA27A,STA27B,"));
    }

    public static string OriginalFindDistinctBeats(String Beats)
    // Accept comma-separated string, return distinct values
    {
        string result = string.Empty;

        try
        {
            result = string.Join(",", Beats.Split(',').Distinct().ToArray());
            result = result.TrimEnd(',');

            if (String.IsNullOrEmpty(result))
            {
                return result;
            }
            else
            {
                return result.TrimEnd(result[result.Length - 1]);
            }

        }
        catch (Exception e)
        {
            return e.ToString();
        }
    }

    public static string NewFindDistinctBeats(String Beats)
    // Accept comma-separated string, return distinct values
    {
        string result = string.Empty;

        try
        {
            result = string.Join(",", Beats.Split(',').Distinct().ToArray());
            result = result.TrimEnd(',');

            return result;
        }
        catch (Exception e)
        {
            return e.ToString();
        }
    }

    public static string NewWithRemoveEmptyFindDistinctBeats(String Beats)
    // Accept comma-separated string, return distinct values
    {
        string result = string.Empty;

        try
        {
            result = string.Join(",", Beats.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries).Distinct().ToArray());

            return result;
        }
        catch (Exception e)
        {
            return e.ToString();
        }
    }
}