Sampling from an array

Question

I have a float array containing 1M floats

I want to do sampling: for each 4 floats I want to take only 1. So i am doing this :

for(int i = 0; i< floatArray.Length; i++) {
    if(i % 4 == 0) {
         resultFloat.Add(floatArray[i])
    }
}

This works fine, but it takes much time to run through all the elements , is there any other methods to make it with better results (if there are any)

Answer 1

I can see two factors that might be slowing down performance.

1. As you have already been offered, you should set the step to 4:

   for (int i = 0; i < floatArray.Length; i += 4)
   {
       resultFloat.Add(floatArray[i]);
   }
   

2. Looks like resultFloat is a list of float. I suggest to use array instead of list, like this:

   int m = (floatArray.Length + 3) / 4;
   
   float[] resultFloat = new float[m];
   
   for (int i = 0, k = 0; i < floatArray.Length; i += 4, k++)
   {
       resultFloat[k] = floatArray[i];
   }
   

Answer 2

Just increment your loop by 4 each iteration instead of by 1:

for(int i = 0; i< floatArray.Length; i+=4)
{
    resultFloat.Add(floatArray[i]);
}