Grouping and the Power of Hierarchical Data

This paper explores what can happen if we organize data hierarchically instead of in a flat rectangular structure. We will see that, given a data analysis platform in which this is easy and natural, a hierarchical structure lets us perform many “data moves” (Erickson et al., 2019) dynamically and transparently. This is not limited to datasets that exhibit what we might call “natural hierarchy.” With many datasets, we can use hierarchy to group and regroup, create summaries, filter data, and even recode categorical values. We conjecture that students who work with hierarchical data will better understand underlying data moves, such as grouping, and be better equipped as advanced students and as informed citizens.