[R] Working With Variables Having Different Lengths

[Rich Shepard]

On Fri, 21 Oct 2011, David Winsemius wrote:

> How are we to determine which lines contain information about the
> "relationships" of param=="TDS" with whatever cases or variable has values
> of "Cond" and "SO4"? Are you really trying to compare two disjoint groups
> on some statistic like the means and std-dev of "quant"? (This would be a
> job for `aggregate`.)

   When I try to select rows based on non-null contents for two values of
'param' I don't have the correct syntax. Perhaps I need to use multiple data
frames instead of a single one?

Rich