Returns the sample skewness of x (calculated with the adjusted Fisher-Pearson standardized
    moment coefficient G1).

    :param x: the time series to calculate the feature of
    :type x: numpy.ndarray
    :return: the value of this feature
    :return type: float

def skewness(x):
    """
    Returns the sample skewness of x (calculated with the adjusted Fisher-Pearson standardized
    moment coefficient G1).

    :param x: the time series to calculate the feature of
    :type x: numpy.ndarray
    :return: the value of this feature
    :return type: float
    """
    if not isinstance(x, pd.Series):
        x = pd.Series(x)
    return pd.Series.skew(x)