Re: [R] find the position of first observation for each subject

I would typically use rle() for this kind of thing: > tmp <- cumsum(rle(id)$lengths) > c(1, tmp[-length(tmp)]+1) [1] 1 4 9 It does assume that all rows for each unique value of id are grouped together, but does not require that the rows be sorted by id. -Don -- Don MacQueen Lawrence Livermor

Re: [R] find the position of first observation for each subject

Also, if the ids are ordered and numeric: which(c(1,diff(ds[,1]))>0) #[1] 1 4 9 A.K. - Original Message - From: arun To: Gallon Li Cc: R help Sent: Thursday, June 13, 2013 9:40 AM Subject: Re: [R] find the position of first observation for each subject HI, Try this:

Re: [R] find the position of first observation for each subject

HI, Try this: ds1<- data.frame(id,time) which(with(ds1,ave(time,id,FUN=seq))==1) #[1] 1 4 9 A.K. - Original Message - From: Gallon Li To: R-help@r-project.org Cc: Sent: Thursday, June 13, 2013 3:56 AM Subject: [R] find the position of first observation for each subject suppose I have

Re: [R] find the position of first observation for each subject

which(!duplicated(ds[, "id"])) Chris Campbell, PhD Tel. +44 (0) 1249 705 450 | Mobile. +44 (0) 7929 628 349 mailto:ccampb...@mango-solutions.com | http://www.mango-solutions.com Mango Solutions, 2 Methuen Park, Chippenham, Wiltshire , SN14 OGB UK -Original Message- From: r-help-boun...@r