Given a dictionary of diversity calculations (keyed by method)
    write out the data to a file.

def write_diversity_metrics(data, sample_ids, fp=None):
    """
    Given a dictionary of diversity calculations (keyed by method)
    write out the data to a file.
    """
    if fp is None:
        fp = "./diversity_data.txt"

    with open(fp, "w") as outf:
        out = csv.writer(outf, delimiter="\t")
        out.writerow(["SampleID", "Group", "Calculation"])
        for group, d in data.iteritems():
            for sid, value in d.iteritems():
                out.writerow([sid, group, value])