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

[William Dunlap]

You may find it easier to use the data.frame method for aggregate
instead of the formula method when you are using vectors of column
names.   E.g.,

  responseVars <- c("mpg", "wt")
  byVars <- c("cyl", "gear")
  aggregate(mtcars[responseVars], by=mtcars[byVars], FUN=median)

gives the same result as

  aggregate(cbind(mpg, wt) ~ cyl + gear, FUN=median, data=mtcars)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Dimitri Liakhovitski
Sent: Thursday, July 14, 2011 1:45 PM
To: David Winsemius
Cc: r-help
Subject: Re: [R] cbind in aggregate formula - based on an existing object (vector)

Thanks a lot!

actually, what I tried to do is very simple - just passing tons of
variable names into the formula. Maybe that "get" thing suggested by
Bert would work...

Dimitri


On Thu, Jul 14, 2011 at 4:01 PM, David Winsemius <dwinsemius at comcast.net> wrote:
> Dmitri:
>
> as.matrix makes a matrix out of the dataframe that is passed to it.
>
> As a further note I attempted and failed for reasons that are unclear to me
> to construct a formula that would (I hoped) preserve the column names which
> are being mangle in the posted effort:
>
> form <- as.formula(paste(
>                     "cbind(",
>                      paste( myvars, collapse=","),
>                      ") ~ group+mydate",
>                      sep=" ") )
>> myvars<-c("value1","value2")
>> example.agg1<-aggregate(formula=form,data=example, FUN=sum)
> Error in m[[2L]][[2L]] : object of type 'symbol' is not subsettable
>> traceback()
> 2: aggregate.formula(formula = form, data = example, FUN = sum)
> 1: aggregate(formula = form, data = example, FUN = sum)
>
>> form
> cbind(value1, value2) ~ group + mydate
>> parse(text=form)
> expression(~
> cbind(value1, value2), group + mydate)
>
> So it seems to be correctly dispatched to aggregate.formula but not passing
> some check or another. Also tried with formula() rather than as.formula with
> identical error message. Also tried including without naming the argument.
>
> --
> David
>
>
> On Jul 14, 2011, at 3:32 PM, Dimitri Liakhovitski wrote:
>
>> Thank you, David, it does work.
>> Could you please explain why? What exactly does changing it to "as matrix"
>> do?
>> Thank you!
>> Dimitri
>>
>> On Thu, Jul 14, 2011 at 3:25 PM, David Winsemius <dwinsemius at comcast.net>
>> wrote:
>>>
>>> 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
>>>>
>>>> ______________________________________________
>>>> R-help at 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.
>>>
>>> David Winsemius, MD
>>> West Hartford, CT
>>>
>>>
>>
>>
>>
>> --
>> Dimitri Liakhovitski
>> Ninah Consulting
>> www.ninah.com
>
> David Winsemius, MD
> West Hartford, CT
>
>



-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com

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