[R] why order doesn't work?

[Bert Gunter]

This has nothing to do with order(). The following also reproduces the behavior:

> test <- data.frame(x=letters[1:5],y = 1:5)
> test[1:5,]$z <- 11:15
Warning message:
In `[<-.data.frame`(`*tmp*`, 1:5, , value = list(x = 1:5, y = 1:5,  :
  provided 3 variables to replace 2 variables
> test
  x y
1 a 1
2 b 2
3 c 3
4 d 4
5 e 5
> test$z <- 11:15
> test
  x y  z
1 a 1 11
2 b 2 12
3 c 3 13
4 d 4 14
5 e 5 15

I don't know what's going on here, but it appears that it has
something to do (again!) with the $ convenience syntax, which is best
avoided, it seems. Instead of the rather convoluted syntax of the
first statement, note that

> test <- data.frame(x=letters[1:5],y = 1:5)
> test[1:5,"z"] <- 11:15
> test
  x y  z
1 a 1 11
2 b 2 12
3 c 3 13
4 d 4 14
5 e 5 15

... works fine.
Have you read "An Intro to R"  where indexing is discussed?  If not,
why not? If so, please follow it. It will help you avoid such
difficulties.

-- Bert

On Fri, Jul 27, 2012 at 1:22 PM, cowboy <dgecon at gmail.com> wrote:
> hi all,
> I want to get a cumsum according to the order of some variable.
> However, it doesnt' work.
> For example,
> **********************
> test<-data.frame(cbind(x=c(3,5,2,6,7),y=c(8,1,4,9,0)))
> test[order(test$x),]$sumy<-cumsum(test[order(test$x),]$y)
> **********************
> R complians Warning message:
> In `[<-.data.frame`(`*tmp*`, order(test$x), , value = list(x = c(2,  :
>   provided 3 variables to replace 2 variables.
>
> while the following
> ***********************
> test$sumy<-cumsum(test[order(test$x),]$y)
> ******************
> gives
>   x y sumy
> 1 3 8    4
> 2 5 1   12
> 3 2 4   13
> 4 6 9   22
> 5 7 0   22
>
> should it gives
>
>   x y sumy
> 1 3 8    12
> 2 5 1   13
> 3 2 4   4
> 4 6 9   22
> 5 7 0   22
>
> What am I missing here?
> thanks,
> Guang
>
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> and provide commented, minimal, self-contained, reproducible code.



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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