[R] adding counter to df by group

[Jim Lemon]

Hi Davide,
You wouldn't be dealing with the Stroop test, would you?

stroop.df<-data.frame(subject=rep(paste("S",1:10,sep=""),each=12),
 color=rep(c("R","G","B"),40),cong=rep(rep(c("C","I"),each=3),20))
stroop.df$colcong<-paste(stroop.df$color,stroop.df$cong,sep="")
stroop.rc<-stroop.df[stroop.df$colcong=="RC",]
table(stroop.df$subject[stroop.df$colcong=="RC"])

Jim

On Thu, May 4, 2017 at 4:24 AM, Davide Piffer <pifferdavide at gmail.com> wrote:
> I need to count the trials in an experiment, separately for each
> subject. I thought about using the function "by" but I could not
> manage to achieve this. Instead, I tried "split" and I got closer to a
> solution but still not getting there yet.
> The following code should create a variable "miniblock" with the
> trial/miniblock number.
> split_cong=split(red_congruent,red_congruent$subject_nr)
> miniblock_cong=lapply(split_cong,seq_along)
> red_congruent$miniblock=unlist(miniblock_cong)
>
> However, I get the following error message: Error in
> `$<-.data.frame`(`*tmp*`, "miniblock", value = c(1L, 2L, 3L,  :
>   replacement has 460 rows, data has 500
>
> Is there a more efficient way to achieve the result? Maybe with "by" or dplyr?
>
> Thanks a lot in advance!
>
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