def METHOD_NAME(self, fields, iteration=None):
    if isinstance(fields, str):
        fields = [fields]
    # load
    group = self.samples_group + '/{name}'
    arrays = {}
    for name in fields:
        if iteration is not None:
            arr = self[group.format(name=name)][int(iteration)]
        else:
            arr = self[group.format(name=name)][:]
        arrays[name] = arr
    return arrays