heat map or matrix plot

[ftr <news ftr free fr>]

Hi,

Can anyone help me please with the following data set that I want to 
plot as a matrix plot or heat map ?

                                    column variable:
                                    not at all    not very much 
somewhat    completely
not at all                    428    49    10    2
not very much          1492    1407    135    14
somewhat                3115    7335    3138    101
completely                874    2668    3079    398

The maybe naive idea is that  the color of the cells change with the 
size of the cell count.

I post my question here as there is no indication in the help of how to 
achieve this.
Maybe the values of the column and the row variables have to be numeric ?

TIA
ftr