js51 / SplitP / 7987845665

        self.data = data

        self.taxa = tuple(taxa)

        self.sub_alignments = dict()

        sub_taxa = tuple(sorted(sub_taxa, key=self.taxa.index))

        try: 

            return self.sub_alignments[sub_taxa]

        except KeyError:

            pass

        sub_taxa_indexer = {taxon: self.taxa.index(taxon) for taxon in sub_taxa}

        sub_taxa_indices = sorted(sub_taxa_indexer.values())

        if not (set(sub_taxa) <= set(self.taxa)):

            raise ValueError("Sub taxa must be a  subset of the taxa")

        all_patterns = set(self.data.keys())

        sub_alignment_data = {}

        while len(all_patterns) > 0:

            pattern = all_patterns.pop()

            trimmed_pattern = "".join(pattern[i] for i in sub_taxa_indices)

            try:

                sub_alignment_data[trimmed_pattern] += self.data[pattern]

            except KeyError:

                sub_alignment_data[trimmed_pattern] = self.data[pattern]

        sub_alignment = Alignment(sub_alignment_data, sub_taxa)

        self.sub_alignments[sub_taxa] = sub_alignment

        return sub_alignment