, replace() random() , , .
x=c(1,2,4,6,7,NA,NA,5,NA,NA,9)
v <- NULL
for(i in 1:length(x)){
if(is.na(x[i])==TRUE)
v <- append(v, i)
}
xnew <- replace(x, v, sample(10, length(v), replace = FALSE))
x
>> 1 2 4 6 7 NA NA 5 NA NA 9
xnew
>> 1 2 4 6 7 5 10 5 4 2 9