How to draw an observation uniformly from a given dataset?

Hi all,

I have two questions stated below:

1. How to draw an observation uniformly from a given data?

For example, I have a dataset (or dataframe) with 10 observations (with a 
set of variables) and I want to "uniformly" select an observation from this 
given dataset, that is, the probability of selecting each observation is 
1/10. 

2. How to do this "combinations"?

source vector = (1,2)
the length of the target vector = 3

My expected outputs should be: 
111, 112, 121, 122, 211, 212, 221, 222.

However, the output from the function of combinations() is only 111, 112, 
122, 222. I can not even use the function permutations() because the length 
of the target vector is larger than the lengthe of the source vector.
Could anybody tell me how to get my expected results? 

Thank you in advance.

Rui