[R] cbind in aggregate formula - based on an existing object (vector)

[David Winsemius]

On Jul 14, 2011, at 3:05 PM, Dimitri Liakhovitski wrote:

> Hello!
>
> I am aggregating using a formula in aggregate - of the type:
> aggregate(cbind(var1,var2,var3)~factor1+factor2,sum,data=mydata)
>
> However, I actually have an object (vector of my variables to be  
> aggregated):
> myvars<-c("var1","var2","var3")
>
> I'd like my aggregate formula (its "cbind" part) to be able to use my
> "myvars" object. Is it possible?
> Thanks for your help!
>

Not sure I have gotten all the way there, but this does work:

example.agg1<-aggregate(as.matrix(example[myvars])~group 
+mydate,sum,data=example)

 > example.agg1
    group     mydate example[myvars]    NA
1 group1 2008-12-01               4   4.2
2 group2 2008-12-01               6   6.2
3 group1 2009-01-01              40  40.2
4 group2 2009-01-01              60  60.2
5 group1 2009-02-01             400 400.2
6 group2 2009-02-01             600 600.2

> Dimitri
>
> Reproducible example:
>
> mydate = rep(seq(as.Date("2008-12-01"), length = 3, by = "month"),4)
> value1=c(1,10,100,2,20,200,3,30,300,4,40,400)
> value2=c(1.1,10.1,100.1,2.1,20.1,200.1,3.1,30.1,300.1,4.1,40.1,400.1)
>
> example<-data.frame(mydate=mydate,value1=value1,value2=value2)
> example$group<-c(rep("group1",3),rep("group2",3),rep("group1", 
> 3),rep("group2",3))
> example$group<-as.factor(example$group)
> (example);str(example)
>
> example.agg1<-aggregate(cbind(value1,value2)~group 
> +mydate,sum,data=example)
> # this works
> (example.agg1)
>
> ### Building my object (vector of 2 names - in reality, many more):
> myvars<-c("value1","value2")
> example.agg1<-aggregate(cbind(myvars)~group+mydate,sum,data=example)
> ### does not work
>
>
> -- 
> Dimitri Liakhovitski
> Ninah Consulting
> www.ninah.com
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT