def standardize_inputs(source, colgroups=None, mean=None, std=None):
    """
    Standardize input features.
    Groups of features could be listed in order to be standardized together.
    source: Pandas.DataFrame or filename of csv file with features
    colgroups: list of lists of groups of features to be standardized together (e.g. bid/ask price, bid/ask size)
    returns Xdf ...Pandas.DataFrame, mean ...Pandas.DataFrame, std ...Pandas.DataFrame
    """
    import itertools
    import types