Suppose I have the sequence:
x = c( 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0)
Is there an elegant way in R to return the start and stop indices of each sequence of 1s?
The answer should be a 2 column array with nRows = number of sequences of 1s:
startIndx = [ 1, 5, 7 ]
stopIndex = [ 2, 5, 9 ]
Thanks.
BSL
Assuming your vector consists of 0 and 1 values:
which(diff(c(0L, x)) == 1L)
#[1] 1 5 7
which(diff(c(x, 0L)) == -1L)
#[1] 2 5 9
Otherwise you'd need something like x <- x == 1L first.
Elegant way is
y <- which(x==1)
startIndx <- y[!(y-1) %in% y]
stopIndex <- y[!(y+1) %in% y]
rbind(startIndx, stopIndex)
# [,1] [,2] [,3]
#startIndx 1 5 7
#stopIndex 2 5 9
Try this:
y = rle(x)
stopIndex = with(y, cumsum(lengths)[values==1])
startIndex = stopIndex - with(y, lengths[values==1]) + 1
#> stopIndex
#[1] 2 5 9
#> startIndex
#[1] 1 5 7
What about this? [editted version according to suggestion of alexis_laz]
library(cgwtools)
res <- seqle(which(as.logical(x)))
rbind(res$values, res$values + res$lengths - 1)
[,1] [,2] [,3]
[1,] 1 5 7
[2,] 2 5 9
How about this:
startIndx<-rev(length(x)-cumsum(rle(rev(x))$lengths)[rle(rev(x))$values==1]+1)
stopIndex<-cumsum(rle(x)$lengths)[rle(x)$values==1]
来源：https://stackoverflow.com/questions/29184297/finding-the-start-and-stop-indices-in-sequence-in-r