st: change value an old variable

[ncdcta00@uniroma2.it]

Dear All,
 I have a variable in a panel that in first year is missing for each  
value. I want to swap this variable by the value of the variable in  
second year? How do it in stata? i try with generate and replace but  
not function.
Thanks a lot for your help
Catia

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/