On Sep 28, 2012, at 11:59 AM, Charles Determan Jr 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"),]
Assume you meant to have a "4" there
>
> group3D=D[group %in% c("3"),]
> group4D=D[group %in% c("3"),]
Ditto. Only makes sense with a "4".
The usual way is to use:
lapply( split(data, interaction(data$LvD, data$group)) ,
fun( subdf) {<do something with subdf>} )
That way you do not end up littering you workspace with subsidiary subsets of
you main data object.
>
> #Times B, S45, FR2, FR8
> you get the idea
>
>
> Is there a more efficient way to subset groups? Thanks for any insight.
>
--
David Winsemius, MD
Alameda, CA, USA
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