如何将通用数组转换为另一种类型？

Question

我仍然试图找到一种快速的方法来如何将TOutput类型的通用数组转换为另一个类型为TInput的数组.我的所有数组都是数字数据类型,但由于C#对经常请求的数字没有类型约束,所以我目前不得不忍受这种约束.建议的方法,比如之前投射到一个物体,似乎极大地减慢了我的演员阵容.目前我有一个大的if/else构造,它检查一个类型并使用指针算法强制转换为已定义的类型,但这是为了将来处理大的方法.Parallel.For似乎是一个摆脱指针和加快速度的好方法,但C#泛型约束似乎仍然存在问题,但下面代码中的Tout仍然是一个问题.这是我的代码:

    public static OutputType[] Cast<InputType, OutputType>(InputType[] inputArray_in)
    {
        var aRange = Partitioner.Create(0, inputArray_in.Length);
        OutputType[] aResult = new OutputType[inputArray_in.Length];

        Parallel.ForEach(aRange, (r) =>
        {
            for (int i = r.Item1; i < r.Item2; i++)
            {
                aResult[i] = (OutputType)(inputArray_in[i]);
            }
        });

        return aResult;
    }

例:

float[] A = { 0.1f, 0.2f, 0.6f };
int []B = Cast<float, int>(A);

在所有情况下,我的数组类型是数值(float,short,double,...),并且大多数情况下,数组大约是512x512个图像,但是在一个卷中大约1000个切片的堆栈中.你有没有机会有一个简单的方法来执行此操作？

测试代码

public static class CastTest
{
    delegate double[] CastMethod(int[] input);

    public static unsafe double[] Cast1(int[] input)
    {
        int N = input.Length;
        double[] output = new double[N];

        for (int i = 0; i < N; i++) output[i] = (double)(input[i]);

        return output;
    }

    public static unsafe double[] Cast2(int[] input)
    {
        int N = input.Length;
        double[] output = new double[N];

        fixed (double* output_pinned = output)
        {
            double* outp = output_pinned;

            fixed (int* input_pinned = input)
            {
                int* inp = input_pinned;

                for (int i = 0; i < N; i++, inp++, outp++) *outp = (double)(*inp);
            }

            return output;
        }
    }

    public static unsafe double[] Cast3(int[] input)
    {
        int N = input.Length;
        double[] output = new double[N];

        fixed (double* output_pinned = output)
        {
            double* outp = output_pinned;

            fixed (int* input_pinned = input)
            {
                int* inp = input_pinned;

                for (int i = 0; i < N; i++) outp[i] = (double)(inp[i]);
            }

            return output;
        }
    }

    public static unsafe double[] Cast4(int[] input)
    {
        int N = input.Length;
        double[] output = new double[N];

        fixed (double* output_pinned = output)
        {
            fixed (int* input_pinned = input)
            {
                for (int i = 0; i < N; i++) output_pinned[i] = (double)(input_pinned[i]);
            }
        }

        return output;
    }

    public static unsafe double[] Cast5(int[] input)
    {
        return Array.ConvertAll<int, double>(input, x => (double)x);
    }

    public static double[] Cast6(int[] input)
    {
        var aRange = Partitioner.Create(0, input.Length);

        int N = input.Length;
        double[] output = new double[N];

        Parallel.ForEach(aRange, (r) =>
            {
                for (int i = r.Item1; i < r.Item2; i++) output[i] = (double)(input[i]);
            });

        return output;
    }

    public unsafe static double[] Cast7(int[] input)
    {
        var aRange = Partitioner.Create(0, input.Length);

        int N = input.Length;
        double[] output = new double[N];

        Parallel.ForEach(aRange, (r) =>
        {
            fixed (double* output_pinned = output)
            {
                double* outp = output_pinned + r.Item1;

                fixed (int* input_pinned = input)
                {
                    int* inp = input_pinned + r.Item1;

                    for (int i = r.Item1; i < r.Item2; i++, outp++, inp++) *outp = (double)(*inp);
                }
            }
        });

        return output;
    }

    public unsafe static double[] Cast8(int[] input)
    {
        var result = (from m in input.AsParallel() select (double)m).ToArray();

        return result;
    }


    public static double[] Cast9(int[] input)
    {
        return  (from m in input select (double)m).ToArray(); 
    }

    public static double[] Cast10(int[] input)
    {
        return (from m in input.AsParallel() select (double)m).ToArray(); 
    }

    public static double[] Cast11(int[] input)
    {
        return new List<double>(input.Select(p => (double)p)).ToArray(); 
    }

    static int[] A = new int[100000];
    const int runs = 10000;

    public static void StartTest()
    {
        TestMethod("1", Cast1);
        TestMethod("2", Cast2);
        TestMethod("3", Cast3);
        TestMethod("4", Cast4);
        TestMethod("5", Cast5);
        TestMethod("6", Cast6);
        TestMethod("7", Cast7);
        TestMethod("8", Cast8);
        TestMethod("9", Cast9);
        TestMethod("10", Cast10);
        TestMethod("11", Cast11);
    }

    static void TestMethod(string Name, CastMethod method)
    {
        var timer = Stopwatch.StartNew();

        for (int i = 0; i < runs; i++) { double[] res = method(A); }

        timer.Stop();

        Console.WriteLine(String.Format("{0}: {1}ms", Name, timer.ElapsedMilliseconds));
    }
}

谢谢马丁

Answer 1

像这样的数字类型之间没有魔术转换(当使用泛型等时); 有一些技巧Convert.ChangeType,或者dynamic,但都涉及一个中间盒/ unbox.

就个人而言,我只是在使用:

float[] A = { 0.1f, 0.2f, 0.6f };
int[] B = Array.ConvertAll(A, x => (int)x);

这将转换逻辑卸载到编译器(使用正确的转换float,int无需中介或反射).但是,它在泛型内部不可用 - 即x => (OutputType)x不起作用.

Answer 2

你尝试过这个吗？

public static TOut[] Cast<TOut,TIn>(TIn[] arr) {
        return arr.Select(x => (TOut)Convert.ChangeType(x,typeof(TOut))).ToArray();
}