[R] Create new data frame with conditional sums

[Bert Gunter]

Well, here's one way to do it:
(dat is your example data frame)

Cutoff <- seq(0, .15, .01)
Pop <- with(dat, sapply(Cutoff, \(p)sum(Totpop[Pct >= p])))

I think there must be a more efficient way to do it with cumsum(), though.

Cheers,
Bert

On Sat, Oct 14, 2023 at 12:53 AM Jason Stout, M.D. <jason.stout using duke.edu> wrote:
>
> This seems like it should be simple but I can't get it to work properly.  I'm starting with a data frame like this:
>
> Tract      Pct          Totpop
> 1              0.05        4000
> 2              0.03        3500
> 3              0.01        4500
> 4              0.12        4100
> 5              0.21        3900
> 6              0.04        4250
> 7              0.07        5100
> 8              0.09        4700
> 9              0.06        4950
> 10           0.03        4800
>
> And I want to end up with a data frame with two columns, a "Cutoff" column that is a simple sequence of equally spaced cutoffs (let's say in this case from 0-0.15 by 0.01) and a "Pop" column which equals the sum of "Totpop" in the prior data frame in which "Pct" is greater than or equal to "cutoff."  So in this toy example, this is what I want for a result:
>
>    Cutoff   Pop
> 1    0.00 43800
> 2    0.01 43800
> 3    0.02 39300
> 4    0.03 39300
> 5    0.04 31000
> 6    0.05 26750
> 7    0.06 22750
> 8    0.07 17800
> 9    0.08 12700
> 10   0.09 12700
> 11   0.10  8000
> 12   0.11  8000
> 13   0.12  8000
> 14   0.13  3900
> 15   0.14  3900
> 16   0.15  3900
>
> I can do this with a for loop but it seems there should be an easier, vectorized way that would be more efficient.  Here is a reproducible example:
>
> dummydata<-data.frame(Tract=seq(1,10,by=1),Pct=c(0.05,0.03,0.01,0.12,0.21,0.04,0.07,0.09,0.06,0.03),Totpop=c(4000,3500,4500,4100,
>                                                                                                              3900,4250,5100,4700,
>                                                                                                              4950,4800))
> dfrm<-data.frame(matrix(ncol=2,nrow=0,dimnames=list(NULL,c("Cutoff","Pop"))))
> for (i in seq(0,0.15,by=0.01)) {
>  temp<-sum(dummydata[dummydata$Pct>=i,"Totpop"])
> dfrm[nrow(dfrm)+1,]<-c(i,temp)
> }
>
> Jason Stout, MD, MHS
> Division of Infectious Diseases
> Dept of Medicine
> Duke University
> Box 102359-DUMC
> Durham, NC 27710
> FAX 919-681-7494
>
>
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>
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