I am trying to find difference of each items of 2 arrays.

int[] items1 = new int[] {10,20,30,40};
int[] items2 = new int[] {20,50,80,100};

resulting array should be
int[] resultItems = {10, 30, 50, 60 }

as the arrays are having more than 10K items, i am trying to avoid looping for better performance. Is there a better way to handle this using LINQ to avoid performance issues?

Thanks!!!

CodePudding user response：

Use multiple threads. Here's a quick sample of subtracting 10.000.000 integers on a single thread:

int []x = new int[100000000];
int []y = new int[100000000];
int []z = new int[100000000];

Random r = new Random();
for (int i = 0; i < 100000000; i  )
{
    x[i] = r.Next();
    y[i] = r.Next();
}

Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();

// This code will be replaced
for (int i = 0; i < 100000000; i  )
    z[i] = y[i] - x[i];

stopWatch.Stop();

TimeSpan ts = stopWatch.Elapsed;
Console.WriteLine(ts);

This takes roughly 500 milliseconds on my hardware.

Now if I create this class:

public static class Subtractor
{
    public static void Subtract(int[] x, int[] y, int[]z, int from, int to)
    {
        for (int i = from; i < to; i  )
            z[i] = y[i] - x[i];
    }
}

and call it on 5 threads:

int []x = new int[100000000];
int []y = new int[100000000];
int []z = new int[100000000];

Random r = new Random();
for (int i = 0; i < 100000000; i  )
{
    x[i] = r.Next();
    y[i] = r.Next();
}

Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();

// Use 5 threads instead of a single for loop
Task task1 = Task.Factory.StartNew(() => Subtractor.Subtract(x, y, z, 0, 20000000));
Task task2 = Task.Factory.StartNew(() => Subtractor.Subtract(x, y, z, 20000000, 40000000));
Task task3 = Task.Factory.StartNew(() => Subtractor.Subtract(x, y, z, 40000000, 60000000));
Task task4 = Task.Factory.StartNew(() => Subtractor.Subtract(x, y, z, 60000000, 80000000));
Task task5 = Task.Factory.StartNew(() => Subtractor.Subtract(x, y, z, 80000000, 100000000));

Task.WaitAll(task1, task2, task3, task4, task5);

stopWatch.Stop();

TimeSpan ts = stopWatch.Elapsed;
Console.WriteLine(ts);

It only takes approx 150 milliseconds.

CodePudding user response：

You can use LINQ nice and simple

var resultItems = items1.Zip(items2, (i1, i2) => i2 - i1).ToArray();

dotnetfiddle

LINQ will not really be much different in performance than iterating the arrays simultaneously. A slightly more efficient implementation would pre-size a list.

var resultItems = new List<int>(items1.Length);
resultItems.AddRange(items1.Zip(items2, (i1, i2) => i2 - i1));

CodePudding user response：

Using one of Select's overload:

var diff = items1.Select((item1, index) => items2[index] - item1).ToArray();