How can pairs of values be stored in a 2D matrix ?

My question is motivated by dealing with pairs of values, like (3,12.5),  (16,2.98), and so on
that are mapped to a cartesian plain (Time, Frequence)
I miss C multidimensional arrays. I am trying to simulate the 3rd dimension by declaring a matrix of lists.

I think the standard R way to do this would be with a 3-dimensional
array.  Many functions are designed to work well with n-dimensional
arrays, including apply and the plyr package.

But R does allow you to make a matrix of lists.

A <- matrix(data ="list", nrow=2, ncol=4)

This creates a matrix of strings (character vector).  What you want is
a matrix of lists, something like this:

  A<-matrix(data=list(), nrow=2,ncol=4)

Then I think all your examples below work.

           -s

PS Note that it does *not* work to write data=NULL, because NULL is
not of class/mode 'list', even though the resulting matrix is filled
with NULL.