how to `.Take()` on a string and get a string at the end?

问题

LINQ to Objects supports queries on string objects but when I use code such as below:

string SomeText = "this is some text in a string";
return SomeText.Take(6).ToString();

All I get is:

System.Linq.Enumerable+<TakeIterator>d__3a`1[System.Char]

This is discussed as an "accident" in this question but this is what I am actually trying to do and I cannot find it through search anywhere.

I know there are other ways to manipulate strings but then I also know you can do some really cool tricks with LINQ and I just would like to know if there is a way to trim a string to a certain length with LINQ?

回答1:

There's no method built in to System.Linq to do this, but you could write your own extension method fairly easily:

public static class StringExtensions
{
    public static string ToSystemString(this IEnumerable<char> source)
    {
        return new string(source.ToArray());
    }
}

Unfortunately, because object.ToString exists on all .NET objects, you would have to give the method a different name so that the compiler will invoke your extension method, not the built-in ToString.

As per your comment below, it's good to question whether this is the right approach. Because String exposes a lot of functionality through its public methods, I would implement this method as an extension on String itself:

/// <summary>
/// Truncates a string to a maximum length.
/// </summary>
/// <param name="value">The string to truncate.</param>
/// <param name="length">The maximum length of the returned string.</param>
/// <returns>The input string, truncated to <paramref name="length"/> characters.</returns>
public static string Truncate(this string value, int length)
{
    if (value == null)
        throw new ArgumentNullException("value");
    return value.Length <= length ? value : value.Substring(0, length);
}

You would use it as follows:

string SomeText = "this is some text in a string";
return SomeText.Truncate(6);

This has the advantage of not creating any temporary arrays/objects when the string is already shorter than the desired length.

回答2:

Just create string

string res = new string(SomeText.Take(6).ToArray());

Also pay attention to string native methods

string res = SomeText.Substring(0, 6);

回答3:

I've run into this myself a few times and use the following:

string.Join(string.Empty,yourString.Take(5));

回答4:

SomeText.Take(6) will returns an IEnumerable of char of char, and ToString method will not return the suspected string you need to call it like the following:

string [] array = SomeText.Take(6).ToArray();
string result = new string(array);

来源：https://stackoverflow.com/questions/6083687/how-to-take-on-a-string-and-get-a-string-at-the-end

标签

linq

string

linq-to-objects

take