public static <T extends Number> OptionalDouble averageDouble(final T[] a, final int fromIndex, final int toIndex) {
        return N.averageDouble(a, fromIndex, toIndex, Fn.numToDouble());
    }
public static < T extends Number > OptionalDouble averageDouble ( final T [ ] a , final int fromIndex , final int toIndex ) { return N . averageDouble ( a , fromIndex , toIndex , Fn . numToDouble ( ) ) ; }
@param a
@param fromIndex
@param toIndex
@return