a simple question--How to select subset of Dataframe in S-Plus

["Liu Zhigang" <email.lzg@gmail.com>]

In SAS, I can use " if " to select my wanted observations.

For example, I want to select the obs satisfy the condition of  x>0 and y<0  (where x and y are variable in a dataset. )

and  operate  with   this subset.In SAS I can do if use following command:

 

[ If x>0 and y<0;  ]

 

But who can tell me how to make this select in S_Plus.

 

Thank you!

 

Liu zhigang

Jilin University