def _get_variants(data):
    """Retrieve set of variant calls to use for heterogeneity analysis.
    """
    supported = ["vardict", "vardict-java", "vardict-perl", "freebayes", "mutect"]
    out = []
    for v in data.get("variants", []):
        if v["variantcaller"] in supported:
            out.append((supported.index(v["variantcaller"]), v))
    out.sort()
    return [xs[1] for xs in out]