[R] loop function within a loop

[Weidong Gu]

It's better to avoid loop in this situation. If you want to reorder
subsets of the data based on event, the follow works

df<-read.table('clipboard',header=TRUE)
sp.or<-lapply(split(df,df$group),function(ldf) ldf[order(ldf$event),])
new.df<-do.call('rbind',sp.or)

Weidong Gu

On Wed, Oct 12, 2011 at 10:55 AM, Sally Zhen <saliluna at gmail.com> wrote:
> Hi all,
>
> I'm working on a loop function for a large dataset which contains 1000
> different groups. I would like to reconstruct the order of events within
> each group by using a loop function in R. (Currently the order of events are
> based on the ascending order of prev_event within the group)
>
>
> A demo data frame:
>
> event       prev_event   group
> 845          0               5360
> 926          153            5360
> 993          234            5360
> 234          845            5360
> 848          926            5360
> 153          993            5360
> 234          0               8765
> 968          234            8765
> 545          968            8765
> 625          111            3334
> 744          181            3334
> 181          227            3334
> 713          625            3334
> 227          713            3334
> 913          0               2329
> 372          119            2329
> 719          189            2329
> 119          324            2329
> 761          355            2329
> 890          372            2329
> 266          719            2329
> 324          761            2329
> 189          890            2329
> 355          913            2329
>
>
> Below is what I have written:
>
> ordering <- vector("list", length(unique(mydata$group)))
> for (j in 1:length(unique(mydata$group))){
> group.j <- mydata[mydata$group == unique(mydata$group)[j], ]
> ordering.j <- c()
> ordering.j[1] <- ifelse(group.j[1, ]$prev_event == 0, group.j[1, ]$event,
> group.j[1, ]$prev_event)
> for (i in 2:nrow(group.j)){
> ordering.j[i] <- group.j[group.j$prev_event == ordering.j[i-1], ]$event}
> ordering[j] <- ordering.j}
> ordering
>
> What I got is:
> Error in ordering.j[i] <- group.j[group.j$prev_event == ordering.j[i -  :
>  replacement has length zero
>> ordering
> [[1]]
> NULL
>
> [[2]]
> NULL
>
> [[3]]
> NULL
>
>
> However, when I accidentally put a typo in the loop function, instead of
> ordering.j[i] <- group.j[group.j$prev_event == ordering.j[i-1], ]$event},
> I put
> ordering.j[i] <- group.j[group.j$prev_event == ordering.j[i-1],
> ]$prev_event},
> The output is a list of 1000 entries, each with the first event within the
> group, and I received the following warning messages:
> [[1]]
> [1] 1.000680e+17
>
> [[2]]
> [1] 1.001390e+17
>
> [[3]]
> [1] 1.001450e+17
>
> 49: In ordering[j] <- ordering.j :
>  number of items to replace is not a multiple of replacement length
> 50: In ordering.j[i] <- group.j[group.j$prev_event ==  ... :
>  number of items to replace is not a multiple of replacement length
>
>
> Why is this happening, and how can I fix it? Any pointer will be greatly
> appreciated!
>
>        [[alternative HTML version deleted]]
>
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