Strange error in R if condition

Question

R newbie here. Can anyone please explain the error in this code?

rankall <- function(outcome, num = "best") {
  data = read.csv("outcome-of-care-measures.csv", colClasses = "character")
  hospital = read.csv("hospital-data.csv", colClasses = "character")
  
  data.hospital = merge(data, hospital, by="Provider.Number")
  
  valid_outcomes = c("heart attack"=11, "heart failure"=17, "pneumonia"=23)
  if (!tolower(outcome) %in% names(valid_outcomes))
    stop("invalid outcome")
  
  state_wise = split(data.hospital, data.hospital$State.x)
  ranked = lapply(state_wise, 
         function(elt) {
            od = order(elt[,valid_outcomes[tolower(outcome)]], elt$Hospital.Name.x)
            elt = elt[od, ]
            deaths = elt[, valid_outcomes[tolower(outcome)]]
            last = match("Not Available", deaths) - 1
            if (num=="best") {
              deaths[1]
            } else if (num =="worst") {
              deaths[last]
            } else if (num >= 1 && num <= last) {
              deaths[num]
            } else {
              NA
            }
  })
  
  df = data.frame(unlist(ranked), names(state_wise))
  names(df) = c("hospital", "state")
  df
}

Function call:

rankall("heart attack", 3)

Error:

Error in if (num >= 1 && num <= last) { :

missing value where TRUE/FALSE needed