<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_bar_data_from_undetermined(self, flowcells):
 """ Get data to plot for undetermined barcodes. """

        bar_data = defaultdict(dict)
        # get undetermined barcodes for each lanes
        for lane_id, lane in flowcells.items():
            try:
                for barcode, count in islice(lane['unknown_barcodes'].items(), 20):
                    bar_data[barcode][lane_id] = count
            except AttributeError:
                pass

        # sort results
        bar_data = OrderedDict(sorted(
            bar_data.items(),
            key=lambda x: sum(x[1].values()),
            reverse=True
        ))
        return OrderedDict(
            (key, value) for key, value in islice(bar_data.items(), 20)
        )