writing function in R

I have written a function in R to rank the hospitals based on the mortality rates for 3 different outcomes(heart attack, heart failure and pneumonia) for each state in the US. The function takes 2 arguments namely the outcome and num(the ranking of a hospital in that state for that outcome). Everything works fine except that I need to include a condition that will return NA if num is greater than the number of hospitals in that state and when I do that it by bypasses all the other if/else if statements. If I don't include that condition, the function works fine. For example,

head(rankall("heart attack", 20), 10)
[1] NA

The required output is:

     hospital_name_all state_list
1                                 <NA>         AK
2       D W MCMILLAN MEMORIAL HOSPITAL         AL
3    ARKANSAS METHODIST MEDICAL CENTER         AR
4  JOHN C LINCOLN DEER VALLEY HOSPITAL         AZ
5                SHERMAN OAKS HOSPITAL         CA
6             SKY RIDGE MEDICAL CENTER         CO
7              MIDSTATE MEDICAL CENTER         CT
8                                 <NA>         DC
9                                 <NA>         DE
10      SOUTH FLORIDA BAPTIST HOSPITAL         FL

    rankall <- function(outcome, num="best"){
    outcome.data <- read.csv("outcome-of-care-measures.csv", colClasses="character")
    outcome.data[, 11] <- as.numeric(outcome.data[, 11]) # heart attack
    outcome.data[, 17] <- as.numeric(outcome.data[, 17]) # heart failure
    outcome.data[, 23] <- as.numeric(outcome.data[, 23]) # pneumonia
    req_outcome <- c("heart attack","heart failure","pneumonia")
    state_list<-sort(unique(outcome.data[,7])) 
    hospital_name_all<- rep("", length(state_list))
       if (!outcome %in% req_outcome) stop("invalid outcome")
       for (i in 1:length(state_list)){
          state.sub<-outcome.data[outcome.data[,7]==state_list[i],]
          limit<-length(state.sub[,2]) 
          if (outcome=="heart attack"){
            mortality.val<-state.sub[,c(2,11)]}
          else if (outcome=="heart failure"){
            mortality.val<-state.sub[,c(2,17)]}
          else if (outcome=="pneumonia"){
            mortality.val<-state.sub[,c(2,23)]}
          if (num=="best"){
              rank.hosp<- mortality.val[order(mortality.val[,2],mortality.val[,1]),]
              best_rank<-min(rank.hosp[,2],na.rm = TRUE)
              min_ind<-which(rank.hosp[,2]==best_rank)
              hospital_name_all[i]<-rank.hosp[min_ind,1]  
              }
          else if (num=="worst"){
              rank.hosp<- mortality.val[order(mortality.val[,2],mortality.val[,1]),]
              worst<-max(rank.hosp[,2],na.rm = TRUE)
              max_ind<-which(rank.hosp[,2]==worst)
              hospital_name_all[i]<-rank.hosp[max_ind,1]  
              } 
           else if (num %in% 1:length(state.sub[,2])){
              hospital_name_all[i]<-mortality.val[,1][order(mortality.val[,2],mortality.val[,1])[num]]
              return(num)
              }
#if (num > limit) {return(NA)}
              }
    rank_hosp_df<-data.frame(hospital_name_all,state_list)
    return(rank_hosp_df)
    } 

Thanks in advance.