[R] How to draw an observation uniformly from a given dataset?
Roger D. Peng
rpeng at jhsph.edu
Wed Sep 8 23:35:52 CEST 2004
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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