# [R] how to extract consecutive subvetors of different lengths from an existing vector and create a matrix

arun smartpink111 at yahoo.com
Tue Feb 25 16:57:58 CET 2014

```Hi,
You could also do:

mat1 <- matrix(NA,ncol=max(n),nrow=length(n))
mat1[cbind(rep(seq_along(n),n),seq_len(sum(n))- rep(cumsum(c(0L,n[-length(n)])),n))] <- y
mat1
A.K.

On Tuesday, February 25, 2014 10:34 AM, arun <smartpink111 at yahoo.com> wrote:
Hi,

One way would be:

res <- t(sapply(split(y,rep(seq_along(n),n)),function(x) {if(length(x) < max(n)) c(x,rep(NA,max(n)-length(x))) else x}))
A.K.

Dear all,

my question regards how to subset an existing vector in
subvectors of different lengths and then create a matrix. See example
below.

I have vectors:

y<-c(1,1,1,0,0,1,1)
n<-c(3,2,2)

and I'd like to create the matrix A of the following form:

1 1  1
0 0 NA
1 1 NA

I'd like to "cut" y sequentially based on information in vector
n, that is, generating 3 subvectors (the first with the first 3 elements
of y, the second with the other 2 elements of y, and the last one with
the latter 2 elements of y) and creating a matrix A (with dimensions,
no.of rows=length(n), no. of col=max(n) and including NAs where
necessary.

Hope to have been clear.

Bex

```