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!
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David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
