def average_df(df, ch_inds):
    """Average dataframe across requested channel inds.

    Parameters
    ----------
    df : pandas.DataFrame
        Container which holds ratio, channels, and peak values.
    ch_inds : list of ints
        Channels to run correlations over.

    Returns
    -------
    avg_df : pandas.DataFrame
        Dataframe, with data averaged across channels.
    """

    # Select relevant rows from df
    avg_df = df.loc[df['Chan_ID'].isin(ch_inds)]

    # Average across selected channels per subject
    avg_df = avg_df.groupby("Subj_ID").mean()

    return avg_df