How to use the phylib.io.array._spikes_in_clusters function in phylib

raise ValueError("Some clusters do not exist.")

        # Find the new cluster number.
        if to is None:
            to = self.new_cluster_id()
        if to < self.new_cluster_id():
            raise ValueError(
                "The new cluster numbers should be higher than {0}.".format(self.new_cluster_id()))

        # NOTE: we could have called self.assign() here, but we don't.
        # We circumvent self.assign() for performance reasons.
        # assign() is a relatively costly operation, whereas merging is a much
        # cheaper operation.

        # Find all spikes in the specified clusters.
        spike_ids = _spikes_in_clusters(self.spike_clusters, cluster_ids)

        up = self._do_merge(spike_ids, cluster_ids, to)
        undo_state = emit('request_undo_state', self, up)

        # Add to stack.
        self._undo_stack.add((spike_ids, [to], undo_state))

        emit('cluster', self, up)
        return up

def spikes_in_template(self, template_id):
        return _spikes_in_clusters(self.spike_templates, [template_id])

def _extend_spikes(spike_ids, spike_clusters):
    """Return all spikes belonging to the clusters containing the specified
    spikes."""
    # We find the spikes belonging to modified clusters.
    # What are the old clusters that are modified by the assignment?
    old_spike_clusters = spike_clusters[spike_ids]
    unique_clusters = _unique(old_spike_clusters)
    # Now we take all spikes from these clusters.
    changed_spike_ids = _spikes_in_clusters(spike_clusters, unique_clusters)
    # These are the new spikes that need to be reassigned.
    extended_spike_ids = np.setdiff1d(changed_spike_ids, spike_ids, assume_unique=True)
    return extended_spike_ids

def spikes_in_clusters(self, clusters):
        """Return the array of spike ids belonging to a list of clusters."""
        return _spikes_in_clusters(self.spike_clusters, clusters)