public static Dataset <double> Mean(this Dataset <double> src) => src.CalcMean(Dataset.Alloc <double>(src.Dim, 1));
public static ref double Mean(this Dataset <double> src, ref double dst) => ref src.CalcMean(ref dst);
public static Dataset <float> Mean(this Dataset <float> src) => src.CalcMean(Dataset.Alloc <float>(src.Dim, 1));