[R] code for Heckman selection with panel data

[Lindy Helfman]

Hello,

Does anyone know of R code that exists to correct for sample selection 
with panel data as in:

J.M. Wooldridge (1995), “Selection Corrections for Panel Data Models 
Under Conditional Mean Independence Assumptions,” Journal of 
Econometrics 68, 115-132.

Many thanks for your consideration,
Lindy