R help - Sep 2006 - Rows of a data frame to matrix

useRs,

I have a data frame where four of the columns of the data frame represent the
values of a two-by-two
matrix. I'd like to, row-by-row, go through the data frame and use the four
columns, in matrix form, to
perform calculations necessary to create new values for variables in the data
frame. My first idea was to
use apply:

apply(as.array(data.frame[,1:4]), 1, matrix, nrow=2)

Though intuitive, this doesn't work. I've stumbled in the dark with
mApply and other functions but can't
find anything in the help that works. This can't be that hard, but it has me
stumped.

Any help greatly appreciated,

Damian

Using the builtin 11x8 anscombe data frame here are
some alternatives:

# 1
# list of 2x2 matrices
lapply(split(anscombe[1:4], 1:nrow(anscombe)), matrix, 2)

# 2
# 2x2x11 array
array(t(anscombe[1:4]), c(2, 2, nrow(anscombe)))

# 3
# to create matrix and perform calculations, e.g. det, all in one step
apply(anscombe[1:4], 1, function(x) det(matrix(x, 2)))



On 9/25/06, Damian Betebenner <damian.betebenner at bc.edu>
wrote:
> useRs,
>
> I have a data frame where four of the columns of the data frame represent
the values of a two-by-two
> matrix. I'd like to, row-by-row, go through the data frame and use the
four columns, in matrix form, to
> perform calculations necessary to create new values for variables in the
data frame. My first idea was to
> use apply:
>
> apply(as.array(data.frame[,1:4]), 1, matrix, nrow=2)
>
> Though intuitive, this doesn't work. I've stumbled in the dark with
mApply and other functions but can't
> find anything in the help that works. This can't be that hard, but it
has me stumped.
>
> Any help greatly appreciated,
>
> Damian
>
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