def net(f, c='close', o=1):
    """Calculate the net change of a given column.

    Parameters
    ----------
    f : pandas.DataFrame
        Dataframe containing the column ``c``.
    c : str
        Name of the column in the dataframe ``f``.
    o : int, optional
        Offset value for shifting the series.

    Returns
    -------
    new_column : pandas.Series (float)
        The array containing the new feature.

    References
    ----------
    *Net change is the difference between the closing price of a security
    on the day's trading and the previous day's closing price. Net change
    can be positive or negative and is quoted in terms of dollars* [IP_NET]_.

    .. [IP_NET] http://www.investopedia.com/terms/n/netchange.asp

    """
    new_column = f[c] - f[c].shift(o)
    return new_column
