[R] Conditional logistic regression for "events/trials" format

[Strickland, Matthew (CDC/CCHP/NCBDDD) (CTR)]

Dear R users,

I have a large individual-level dataset (~700,000 records) which I am
performing a conditional logistic regression on. Key variables include
the dichotomous outcome, dichotomous exposure, and the stratum to which
each person belongs. 

Using this individual-level dataset I can successfully use clogit to
create the model I want. However reading this large .csv file into R and
running the models takes a fair amount of time.

Alternatively, I could choose to "collapse" the dataset so that each row
has the number of events, number of individuals, and the exposure and
stratum. In SAS they call this the "events/trials" format. This would
make my dataset much smaller and presumably speed things up.

So my question is: can I use clogit (or possibly another function) to
perform a conditional logistic regression when the data is in this
"events/trials" format? I am using R version 2.5.0.

Thank you very much, 
Matt Strickland
Birth Defects Branch
U.S. Centers for Disease Control