[R] Array Manipulation

[cdsmith@ksu.edu]

I have a data set that looks like the following:
ID  Responce
1   57
1   63
1   49
2   31
2   45
2   67
2   91
3   56
3   43
4   23
4   51
4   61
4   76
4   68
5   34
5   35
5   45
I used sample(unique(ID)) to select a sample if ID's, say, (1,4,5).  Now
I want to pull out the rows with ID's 1, 4, and 5.  I've tried forceing
the matrix into a vector but it does not create and appropriate vector.
 I've also tried the if statment but it didn't work right either.  Any
suggestions?