使用同一元素的多个副本初始化C#数组 [英] Initializing a C# array with multiple copies of the same element

问题描述

例如，在C ++标准模板库(STL)中，可以使用以下构造函数创建一个由相同元素的多个副本组成的矢量:

In the C++ Standard Template Library (STL), it is possible for example to create a vector consisting of multiple copies of the same element, using this constructor:

std::vector<double> v(10, 2.0);

这将创建一个10倍的向量，最初设置为2.0.

This would create a vector of 10 doubles, initially set to 2.0.

我想在C#中做类似的事情，更具体地说，创建一个 n 双精度数组，并将所有元素初始化为相同的值 x .

I want to do a similar thing in C#, more specifically creating an array of n doubles with all elements initialized to the same value x.

我根据通用集合和LINQ提出了以下一种方法:

I have come up with the following one-liner, relying on generic collections and LINQ:

double[] v = new double[n].Select(item => x).ToArray();

但是，如果一个局外人会阅读这段代码，我认为代码实际上不会立即生效.我还担心性能，我想通过 for 循环初始化数组元素会更快(尽管我没有检查).有人知道更干净和/或更有效的方法来执行此任务吗?

However, if an outsider would read this code I don't think it would be immediately apparent what the code actually does. I am also concerned about the performance, I suppose it would be faster to initialize the array elements via a for loop (although I haven't checked). Does anybody know of a cleaner and/or more efficient way to perform this task?

推荐答案

这怎么办?

double[] v = Enumerable.Repeat(x, n).ToArray();

我只是做了一个小型基准测试；创建一个1000个数组(每个数组包含100000个元素)，使用循环的速度是Enumerable.Repeat的三倍.

I just did a small benchmark; to create 1000 arrays of 100000 elements each, using a loop is about 3 times faster that Enumerable.Repeat.

Repeat 
00:00:18.6875488 

Loop 
00:00:06.1628806 

因此，如果性能至关重要，则应该选择循环.

So if performance is critical, you should prefer the loop.

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