如何在C＃中使用LINQ返回不同单词的列表？

Question

The goal is to sort through a text (ie a speech) and output a list of the distinct words in the speech to a textbox. I have read through a lot of tips on the boards and played around a lot but at this point am at that point where I am more confused then when I started. Here is my code

   private void GenerateList(string[] wordlist)
    {
       List<string> wordList = new List<string>();

        for (int i = 0; i < wordlist.Length; i++)
        {
            wordList.Add(wordlist[i]);
        }

        var uniqueStr = from item in wordList.Distinct().ToList()
                        orderby item
                        select item;


        for (int i = 0; i < uniqueStr.Count(); i++ )
        {
            txtOutput.Text = uniqueStr.ElementAt(i) + "\n";
        }

    }

At this point I am getting a return of one word. For the text I am using (the gettysburg address) it is the word "year" and it is the only instance of that word in the text.

I am passing the function each individual word loaded into a string array that is then put into a list (which may be redundant?).

Answer 1

I hope this does what you need in a simple and efficient manner (using .Dump() from LINQPad)

void Main()
{
    // can be any IEnumerable<string> including string[]
    var words = new List<string>{"one", "two", "four", "three", "four", "a", "z"};

    words.ToDistinctList().Dump();

    // you would use txtOutput.Text = words.ToDistinctList()
}

static class StringHelpers
{
    public static string ToDistinctList(this IEnumerable<string> words)
    {
        return string.Join("\n", new SortedSet<string>(words));
    }
}

Answer 2

A few tips regarding your question:

• There is no reason to turn the array into list, because LINQ extension methods are defined on IEnumerable<T> , which is implemented by both the array and the list
• Make sure that all letters are in the same case - use ToLower, for instance
• You are overwriting txtOutput.Text in every iteration. Instead of setting the new value, append new part to the existing value

Here is the simple piece of code which produces the output you wanted:

IEnumerable<string> distinct =
    wordList
    .Select(word => word.ToLower())
    .Distinct()
    .OrderBy(word => word);

txtOutput.Text = string.Join("\n", distinct.ToArray());

On a related note, here is a very simple LINQ expression which returns distinct words from a text, where the whole text is specified as one string:

public static IEnumerable<string> SplitIntoWords(this string text)
{

    string pattern = @"\b[\p{L}]+\b";

    return
        Regex.Matches(text, pattern)
            .Cast<Match>()                          // Extract matches
            .Select(match => match.Value.ToLower()) // Change to same case
            .Distinct();                            // Remove duplicates

}

You can find more variations of regex pattern for the same problem here: Regex and LINQ Query to Split Text into Distinct Words

Answer 3

Here's how I'd simplify your code, as well as achieve what you want to achieve.

private void GenerateList(string[] wordlist)
{
   List<string> wordList = wordlist.ToList(); // initialize the list passing in the array


    var uniqueStr = from item in wordList.Distinct().ToList()
                    orderby item
                    select item;


    txtOutput.Text = String.Join("\n", uniqueStr.ToArray());
}

Answer 4

You can use the fact that the StringBuilder class has a fluent interface along with LINQ to simplify this greatly.

First, you can create the StringBuilder and concatenate all of the words into the same instance like so:

// The builder.
var builder = new StringBuilder();

// A copy of the builder *reference*.
var builderCopy = builder;

// Get the distinct list, order by the string.
builder = wordList
    // Get the distinct elements.
    .Distinct()
    // Order the words.
    .OrderBy(w => w).
    // Append the builder.
    Select(w => builderCopy.AppendLine(word)).
    // Get the last or default element, this will
    // cycle through all of the elements.
    LastOrDefault();

// If the builder is not null, then assign to the output, otherwise,
// assign null.
txtOutput.Text = builder == null ? null : builder.ToString();

Note, you don't have to actually materialize the list, as wordList is already a materialized list, it's an array (and as a side note, typed arrays in C# implement the IList<T> interface ).

The AppendLine method (and most of the methods on StringBuilder ) return the instance of the StringBuilder that the operation was performed on, which is why the LastOrDefault method call works; simply call the operation and return the result (each item returned will be the same reference).

The builderCopy variable is used to avoid access to a modified closure (it never hurts to be safe).

The null check at the end is for the case where wordList doesn't contain any elements. In this case, the call to LastOrDefault will return null.