Thank you Jeff,

The main purpose I am looking to use these subsets for is to do comparisons
between groups and/or timepoints within groups.  For example the difference
in means between 3 and 4, or the percent difference between group L an D
within group 3.  The code I have provided is almost exactly as used
although David accurately noted I mistakenly typed '3' when I intended to
put '4'.  I am just looking for some general guidance in improving how I go
about my code.  Because there are so many subgroups that can be formed with
three layers of groups, it simply becomes a clutter and I wanted to learn
if there was a 'better' way to organize groups for comparisons.  Does that
help clarify?

Thanks again,
Charles

On Fri, Sep 28, 2012 at 4:25 PM, Jeff Newmiller <jdnewmil@dcn.davis.ca.us>wrote:

> You have not specified the objective function you are trying to optimize
> with your term "efficient", or what you do with all of these subsets once
> you have them.
>
> For notational simplification and completeness of coverage (not
> necessarily computational speedup) you might want to look at "tapply" or
> ddply/dlply from the plyr package. If you build lists of subsets you can
> index into them according to grouping value. You can use expand.grid to
> build all permutations of grouping values to use as indexes into those
> lists of subsets.
>
> To reiterate, you have not indicated what you want to do with these
> subsets, so there could be special-purpose functions that do what you want.
>  As always, reproducible code leads to reproducible answers. :)
> ---------------------------------------------------------------------------
> Jeff Newmiller                        The     .....       .....  Go Live...
> DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
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> ---------------------------------------------------------------------------
> Sent from my phone. Please excuse my brevity.
>
> Charles Determan Jr <deter088@umn.edu> wrote:
>
> >Hello R users,
> >
> >This is more of a convenience question that I hope others might find
> >useful
> >if there is a better answer.  I work with large datasets that requires
> >multiple parsing stages for different analysis.  For example, compare
> >group
> >3 vs. group 4.  A more complicated comparison would be time B in group
> >3 of
> >group L with B in group 4 of group L.  I normally subset each group
> >with
> >the following type of code.
> >
> >data=read(...)
> >
> >#L v D
> >L=data[LvD %in% c("L"),]
> >D=data[LvD %in% c("D"),]
> >
> >#Groups 3 and 4 within L and D
> >group3L=L[group %in% c("3"),]
> >group4L=L[group %in% c("3"),]
> >
> >group3D=D[group %in% c("3"),]
> >group4D=D[group %in% c("3"),]
> >
> >#Times B, S45, FR2, FR8
> >you get the idea
> >
> >
> >Is there a more efficient way to subset groups?  Thanks for any
> >insight.
> >
> >Regards,
> >Charles
> >
> >       [[alternative HTML version deleted]]
> >
> >______________________________________________
> >R-help@r-project.org mailing list
> >https://stat.ethz.ch/mailman/listinfo/r-help
> >PLEASE do read the posting guide
> >http://www.R-project.org/posting-guide.html
> >and provide commented, minimal, self-contained, reproducible code.
>
>

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