Question

I’m looking for an elegant way to implement a moving average filter in c#. Now, that would be easy, but at the borders, the averaging window shall wrap around the start/end. This kind of made my code ugly and unintuitive, and I was wondering whether there was a smarter way to solve this using LINQ or so.

So what I currently have is:

// input is a List<double> y, output is List<double> yfiltered
int yLength = y.Count;
for (int i = 0; i < yLength; i++)
{
    double sum = 0.0;
    for (int k = i - halfWindowWidth; k <= i + halfWindowWidth; k++)
    {
        if (k < 0)
        {
            // k is negative, wrap around
            sum += y[yLength - 1 + k];
        }
        else if (k >= yLength)
        {
            // k exceeds y length, wrap around
            sum += y[k - yLength];
        }
        else
        {
            // k within y.Count
            sum += y[k];
        }
    }
    yfiltered[i] = sum / (2 * halfWindowWidth + 1);
}

Answer 1

Expanding on my comment, you could use the mod (%) operator to get k to wrap
from 0 to ylength - 1

    // input is a List<double> y, output is List<double> yfiltered
    int yLength = y.Count;
    for (int i = 0; i < yLength; i++)
    {
        double sum = 0.0;
        for (int k = i - halfWindowWidth; k <= i + halfWindowWidth; k++)
        {
            sum += y[(k + yLength) % yLength];
        }
        yfiltered[i] = sum / (2 * halfWindowWidth + 1);
    }