def filter_df_by_cluster(df, clusters, number):
    """ 
    Select only the members of a defined cluster.
    
    :param df: pandas dataframe with samples/subjects as index and features as columns.
    :param dict clusters: clusters dictionary from get_dendrogram function if div_clusters option was True.
    :param int number: cluster number (key).
    :return: Pandas dataframe with all the features (columns) and samples/subjects belonging to the defined cluster (index).
    """
    return df[df.index.isin(clusters[number])]