Dynamic input matrix

Hi there

I've scoured stackoverflow and the old google group and can't seem to find anything to answer this question.

I am trying to create a shiny app that takes an R x C matrix as input, but the user first tells shiny what the value of R and C are.

As an example, let's say the user is going to evaluate 7 toy brands based on three attributes (cost, color, and "Made in the USA", for example). The resulting input would be a 7 x 3 matrix.

The next user may be evaluating something completely different. I'd like the app to be flexible enough to display a matrix of text boxes, of user-defined size.

Is there any way to do this?