[R] flatten a matrix and unflatten it

[Huntsinger, Reid]

If you can rearrange things to work column-wise rather than row-wise, then

dim(x) <- NULL

makes a matrix into a vector by concatenating columns, and

dim(x) <- c(m,n)

makes the vector x into a matrix with column 1 equal to the first m elements
of x, column 2 equal to the next m elements, etc.

If you need row-major order, you can do

x <- as.vector(t(x)) 

and 

x <- matrix(x,nrow=m,ncol=n,byrow=TRUE)

Reid Huntsinger

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Bill Simpson
Sent: Monday, March 21, 2005 4:44 PM
To: r-help
Subject: [R] flatten a matrix and unflatten it


I want to flatten a matrix and unflatten it again. Please tell me how to 
do it.

1. given a matrix:
x1 y1 z1
x2 y2 z2
...
xk yk zk
convert it to a vector:
x1, y1, z1, x2, y2, z2, ..., xk, yk, zk

2. given a vector:
x1, y1, z1, x2, y2, z2, ..., xk, yk, zk
convert it to a matrix
x1 y1 z1
x2 y2 z2
...
xk yk zk

It is known that the number of dimensions is 3.

Thanks for any help!

Bill

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