Simple NA problem

["Jan Ivanouw" <ivanouw@post8.tele.dk>]

I am sorry I can't find the solution to this simple problem. Can anyone help?

 

I have a (large) data frame with missing values, like this:

 

a       b     c
1       3     5
NA    9     2
3       5     2
NA    8     6
5       3     7

 

Based on non-missing values of variable a, I want it changed to

 

a     b     c
1     3     5
3     5     2
5     3     7

 

 

Thank you

 

Jan Ivanouw PhD

University of Copenhagen

Denmark