IEnumerable的＆LT;焦炭＆GT;字符串 [英] IEnumerable<char> to string

问题描述

我从来没有碰到这个偶然发现过，但我现在已经和很惊讶，我找不到一个非常简单的方法来转换一个的IEnumerable＆LT;焦炭＆GT; 来一个字符串。

我能想到的最好的办法就是字符串str =新的字符串（myEnumerable.ToArray（））; ，但对我来说，好像这将创建一个新的的char [] ，然后创建一个新的字符串从，这似乎是昂贵的。

我会一直以为这是建立在.NET Framework中的某处常见功能。有没有一种简单的方法来做到这一点？

对于那些有兴趣，我想用这个的原因是使用LINQ过滤字符串：

 字符串allowedString =新的字符串（inputString.Where（C =＆GT; allowedChars.Contains（C））ToArray的（））;
 

解决方案

您可以使用 String.Concat（） 。

  VAR allowedString = String.Concat（
    inputString.Where（C =＆GT; allowedChars.Contains（C））
）;
 

买者：这种方法会有一些性能问题。看来， String.Concat 不字符的特例集合如此看来它执行，如果每个字符被转换为字符串然后再连接（ <一个HREF =htt​​p://referencesource-beta.microsoft.com/mscorlib/a.html#630a858d9b6f4c5d>，它实际上确实 ）。当然这给你一个内建的方式来完成这个任务，但它可以做的更好。

我不认为有框架内的任何实现，将特殊情况字符所以你必须实现它。一个简单的循环附加字符的字符串生成器是很简单的创建。

---

下面是一些基准，我花了开发计算机上，它看起来是正确的。

百万迭代上300字符序列在32位版本编译：

ToArrayString：00：00：03.1695463
的concat：00：00：07.2518054
StringBuilderChars：00：00：03.1335455
StringBuilderStrings：00：00：06.4618266

 静态只读的IEnumerable＆LT;焦炭＆GT; SEQ = Enumerable.Repeat（'一个'，300）;静态字符串ToArrayString（IEnumerable的＆LT;焦炭＆GT;的CharSequence）
{
    返回新的String（charSequence.ToArray（））;
}静态字符串连接（IEnumerable的＆LT;焦炭＆GT;的CharSequence）
{
    返回String.Concat（CharSequence的）;
}静态字符串StringBuilderChars（IEnumerable的＆LT;焦炭＆GT;的CharSequence）
{
    VAR SB =新的StringBuilder（）;
    的foreach（在CharSequence的变种C）
    {
        sb.Append（C）;
    }
    返回sb.ToString（）;
}静态字符串StringBuilderStrings（IEnumerable的＆LT;焦炭＆GT;的CharSequence）
{
    VAR SB =新的StringBuilder（）;
    的foreach（在CharSequence的变种C）
    {
        sb.Append（c.ToString（））;
    }
    返回sb.ToString（）;
}
 

I've never stumbled across this before, but I have now and am surprised that I can't find a really easy way to convert an IEnumerable<char> to a string.

The best way I can think of is string str = new string(myEnumerable.ToArray());, but, to me, it seems like this would create a new char[], and then create a new string from that, which seems expensive.

I would've thought this would be common functionality built into the .NET framework somewhere. Is there a simpler way to do this?

For those interested, the reason I'd like to use this is to use LINQ to filter strings:

string allowedString = new string(inputString.Where(c => allowedChars.Contains(c)).ToArray());

解决方案

You can use String.Concat().

var allowedString = String.Concat(
    inputString.Where(c => allowedChars.Contains(c))
);

Caveat: This approach will have some performance implications. It seems that String.Concat doesn't special case collections of characters so it seems that it performs as if every character was converted to a string then concatenated (and it actually does). Sure this gives you a builtin way to accomplish this task, but it could be done better.

I don't think there are any implementations within the framework that will special case char so you'll have to implement it. A simple loop appending characters to a string builder is simple enough to create.

---

Here's some benchmarks I took on a dev machine and it looks about right.

1000000 iterations on a 300 character sequence on a 32-bit release build:

ToArrayString:        00:00:03.1695463
Concat:               00:00:07.2518054
StringBuilderChars:   00:00:03.1335455
StringBuilderStrings: 00:00:06.4618266

static readonly IEnumerable<char> seq = Enumerable.Repeat('a', 300);

static string ToArrayString(IEnumerable<char> charSequence)
{
    return new String(charSequence.ToArray());
}

static string Concat(IEnumerable<char> charSequence)
{
    return String.Concat(charSequence);
}

static string StringBuilderChars(IEnumerable<char> charSequence)
{
    var sb = new StringBuilder();
    foreach (var c in charSequence)
    {
        sb.Append(c);
    }
    return sb.ToString();
}

static string StringBuilderStrings(IEnumerable<char> charSequence)
{
    var sb = new StringBuilder();
    foreach (var c in charSequence)
    {
        sb.Append(c.ToString());
    }
    return sb.ToString();
}

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