[R] How to draw an observation uniformly from a given dataset?

[Roger D. Peng]

wanr at ucalgary.ca wrote:
> 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. 

Sample the indices, as in

idx <- sample(1:10, 1)
data[idx, ]

> 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
> 
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