[R] why order doesn't work?
William Dunlap
wdunlap at tibco.com
Fri Jul 27 22:47:09 CEST 2012
> 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)
is asking a bit too much of R. If you add the line
test$sumy <- numeric(nrow(test))
between those lines you get what you want.
Here are the details. The nested replacement expression
dataFrame[subscript, ]$component <- value
is treated as the sequence of expressions
TMP <- dataFrame[subscript,]
TMP$component <- value
dataFrame[subscript, ] <- TMP
If dataFrame has no column named 'component' then the last
expression involves trying to replace some rows of the n-column
data.frame dataFrame by the contents of the (n+1)-column data.frame
TMP and R will not do that.
By the way, drop the cbind from
data.frame(cbind(x=..., y=...))
and just use
data.frame(x=..., y=...)
The cbind() slows things down, wastes memory, and can give
surprising results (when x and y have different classes).
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
> Behalf Of cowboy
> Sent: Friday, July 27, 2012 1:23 PM
> To: r-help at r-project.org
> Subject: [R] why order doesn't work?
>
> hi all,
> I want to get a cumsum according to the order of some variable.
> However, it doesnt' work.
> For example,
> **********************
> test<-data.frame(cbind(x=c(3,5,2,6,7),y=c(8,1,4,9,0)))
> test[order(test$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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