> -----Original Message----- > From: r-help-boun...@r-project.org > [mailto:r-help-boun...@r-project.org] On Behalf Of Gregory Gentlemen > Sent: Wednesday, January 27, 2010 9:31 AM > To: r-help@r-project.org > Subject: [R] Function for describing segements in sequential data > > Dear R-users, > > Say that I have a sequence of zeroes and ones: > > x <- c(1,1,1,0,0,0,0,1,1,1,0,0,0,0,1,1,1,0,0,0,0) > > The sequences of ones represent segments and I want to report > the starting and endpoints of these segments. For example, in > 'x', the first segment starts at location 1 and ends at 3, > and the second segment starts at location 8 and ends at > location 10. Is there an efficient way of doing this in R > without having to right a bunch of if-else conditions? I know > the rle function will report the length of the segments but > not the endpoints.
You can use expressions based on cumsum(rle(x)$lengths) or, more directly, on the following functions isFirstInRun <- function(x)c(TRUE, x[-1]!=x[-length(x)]) isLastInRun <- function(x)c(x[-1]!=x[-length(x)], TRUE) which do part of what rle() does. E.g., > which(isFirstInRun(x) & x==1) # starting positions of runs of 1's [1] 1 8 15 > which(isLastInRun(x) & x==1) # ending positions of runs of 1's [1] 3 10 17 Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > > Thanks in advance. > > Gregory Gentlemen > > > > > __________________________________________________________________ > [[elided Yahoo spam]] > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@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. > ______________________________________________ R-help@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.