I have a numeric called area of length 166860. This consists of 412 different elements, most of length 405 and some of length 809. I have their start and end ids.

My goal is to extract them and put them in a matrix/data frame with 412 columns

Right now, I'm trying this code:

m = matrix(NA,ncol=412, nrow=809)
for (j in 1:412){
temp.start = start.ids[j]
temp.end = end.ids[j]
m[,j] = area[temp.start:temp.end]
}

But I just end up with this error message:

"Error in m[, j] = area[temp.start:temp.end] : number of items to replace is not a multiple of replacement length"

Here's a quite easy approach:

Example data:

area <- c(1:4, 1:5, 1:6, 1:3)
# [1] 1 2 3 4 1 2 3 4 5 1 2 3 4 5 6 1 2 3

start.ids <- which(area == 1)
# [1]  1  5 10 16

end.ids <- c(which(area == 1)[-1] - 1, length(area))
# [1]  4  9 15 18

Create a list with one-row matrices:

mats <- mapply(function(x, y) t(area[seq(x, y)]), start.ids, end.ids)
# [[1]]
#      [,1] [,2] [,3] [,4]
# [1,]    1    2    3    4
#
# [[2]]
#      [,1] [,2] [,3] [,4] [,5]
# [1,]    1    2    3    4    5
#
# [[3]]
#      [,1] [,2] [,3] [,4] [,5] [,6]
# [1,]    1    2    3    4    5    6
#
# [[4]]
#      [,1] [,2] [,3]
# [1,]    1    2    3

Use the function rbind.fill.matrix from the plyr package to create the matrix and transpose it (t):

library(plyr)
m <- t(rbind.fill.matrix(mats))
#    [,1] [,2] [,3] [,4]
# 1    1    1    1    1
# 2    2    2    2    2
# 3    3    3    3    3
# 4    4    4    4   NA
# 5   NA    5    5   NA
# 6   NA   NA    6   NA