Many problems in data management center on relating values to values in other observations, either within a dataset as a whole or within groups such as panels. This column reviews some basic Stata techniques helpful for such tasks, including the use of subscripts, summarize, by:, sum(), cond(), and egen. Several techniques exploit the fact that logical expressions yield 1 when true and 0 when false. Dividing by zero to yield missings is revealed as a surprisingly valuable device.
