[R] loop function within a loop

[David Winsemius]

On Oct 12, 2011, at 10:55 AM, Sally Zhen 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.

Not generally a good first strategy in R.

> (Currently the order of events are
> based on the ascending order of prev_event within the group)

Wouldn't this just be:

dfrm[order(dfrm$group, dfrm$event), ]

(Ascending is the default ordering.)
-- 
David.
>
>
> 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]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT