Generating input population for microsimulation

Hi all,

I've been struggling with some code and was wondering if you all could help.

I am trying to generate a theoretical population of P people who are housed within X different units. Each unit follows the same structure- 10 people per unit, 8 of whom are junior and two of whom are senior. I'd like to create a unit ID and a unique identifier for each person (person ID, PID) in the population so that I have a matrix that looks like:

???? unit_id pid senior
? [1,]????? 1?? 1????? 0
? [2,]????? 1?? 2????? 0
? [3,]????? 1?? 3????? 0
? [4,]????? 1?? 4????? 0
? [5,]????? 1?? 5????? 0
? [6,]????? 1?? 6????? 0
? [7,]????? 1?? 7????? 0
? [8,]????? 1?? 8????? 0
? [9,]????? 1?? 9????? 1
? [10,]??? 1?? 10?? 1
...

I came up with the following code, but am having some trouble getting it to populate my matrix the way I'd like.

world <- function(units, pop_size, unit_size){
??? pid <- rep(0,pop_size) #person ID
??? senior <- rep(0,pop_size) #senior in charge
??? unit_id <- rep(0,pop_size) #unit ID
???
??? ??? for (i in 1:pop_size){
??? ??? for (f in 1:units)??? {?
??? ??? senior[i] = sample(c(1,1,0,0,0,0,0,0,0,0), 1, replace = FALSE)
??? ??? pid[i] = sample(c(1:10), 1, replace = FALSE)
??? ??? unit_id[i] <- f
??? ??? ??? ??? }}???
??? data <- cbind(unit_id, pid, senior)
???
??? return(data)
??? }

??? world(units = 10,pop_size = 100, unit_size = 10) #call the function



The output looks like:
???? unit_id pid senior
? [1,]????? 10?? 7????? 0
? [2,]????? 10?? 4????? 0
? [3,]????? 10? 10????? 0
? [4,]????? 10?? 9????? 1
? [5,]????? 10? 10????? 0
? [6,]????? 10?? 1????? 1
...

but what I really want is to generate is 10 different units with two seniors per unit, and with each person in the population having a unique identifier.

I thought a nested for loop was one way to go about creating my data set of people and families, but obviously I'm doing something (or many things) wrong. Any suggestions on how to fix this? I had been focusing on creating a person and assigning them to a unit, but perhaps I should create the units and then populate the units with people?

Thanks so much in advance.

Emma