Default groups are integers but occasionally expected to be strings

[jonahpearl]

In the analysis-visualization notebook, in the cell for exporting TM's:
group_index = next(i for i, g in enumerate(group) if g == selected_group)
and for me, group is defaults [0, 1, 2, 3, 4, 5, 6].

But then later in the same cell:
group_trans.to_csv(join(save_path, selected_group + '_trans.csv'), index=False)
fails because it can't add an int to a string.

Simple fix: add str() here. But maybe double check to make sure this dual conventioning isn't happening elsewhere.