Dear sir,

If I have a vector as:
>y <- c(1:4)
and a matrix as:
>x <- matrix (5:12, nrow=4, ncol=2)

Then I create a data frame as:
>t <- data.frame(y, x)

R will generate a data frame of 3 columns
>names(t)
> "y"  "X1" "X2"
>is.vector(t$X1) returns TRUE
> is.vector(t$X2) returns TRUE
R splits the columns of a matrix into column vectors automatically.

How should I create a data frame of t$y & t$x such that
>is.vector(t$y) returns TRUE
>is.matrix(t$x) returns TRUE
That is, how to make x column of the data frame a matrix? Just like the test data ¨gasoline〃 in your PLS package:
>library(pls)
>data(yarn)
>is.vector(density) returns TRUE
>is.matrix(NIR) returns TURE (NIR is a matrix)

Best regards,
Shaowen Cheng

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