[R] Drawing a sample based on certain condition

[Brian Smith]

Hi,

For my analytical work, I need to draw a sample of certain sample size
from a denied population, where population members are marked by
non-negative integers, such that sum of sample members if fixed. For
example,

Population = 0:100
Sample_size = 10
Sample_Sum = 20

Under this setup if my sample members are X1, X2, ..., X10 then I
should have X1+X2+...+X10 = 20

Sample drawing scheme may be with/without replacement

Is there any R function to achieve this? One possibility is to employ
naive trial-error approach, but this doesnt seem to be practical as it
would take long time to get the final sample with desired properties.

Any pointer would be greatly appreciated.