[R] What is the equivalent of column.prods() from S in R?

[David Winsemius]

On Nov 29, 2009, at 12:20 AM, Peng Yu wrote:

> On Sat, Nov 28, 2009 at 11:00 PM, David Winsemius
> <dwinsemius at comcast.net> wrote:
>>
>> On Nov 28, 2009, at 11:28 PM, Peng Yu wrote:
>>
>>> On Mon, Nov 9, 2009 at 8:35 PM, David Winsemius <dwinsemius at comcast.net 
>>> >
>>> wrote:
>>>>
>>>> On Nov 9, 2009, at 8:43 PM, Peng Yu wrote:
>>>>
>>>>> Chambers' book Statistical Models in S mentioned  
>>>>> 'column.prods()'. But
>>>>> I don't find it in R. I'm wondering if there is an equivalent in  
>>>>> R?
>>>>
>>>> ??rowProds
>>>> ??colProds
>>>>
>>>> (They are in both fUtilities and timeSeries.)
>>>
>>> Are you sure that colProds() is equivalent to column.prods()? It  
>>> seems
>>> that column.prods() should be a very basic function in S, but I have
>>> to load a package in order to call colProds().
>>>
>>> I don't see how to construct a matrix give terms as mentioned in the
>>> book. Would you please give me some examples?
>>
>> Page numbers? Specifics? ....something to go on?
>
> As is mentioned in the appendix of the book, it is on page 38.

It's a chapter on the internal representation of models. So, no, I  
agree, the colProds function does not do what column.prods did in S  
which was to represent interaction terms.  The terms.object help page  
says these are different than in S. I suspect that the function you  
want is model.matrix. An example with from its help page:

dd <- data.frame(a = gl(3,4), b = gl(4,1,12))# balanced 2-way
options("contrasts")
model.matrix( ~ a + b, dd)
# and then the "product" design matrix
model.matrix( ~ a * b, dd)


-- 
David Winsemius, MD
Heritage Laboratories
West Hartford, CT