agecount.R

agecount <- function(age = NULL) {
  ## Check that "age" is non-NULL; else throw error
  if(is.null(age)){
    stop("Cause cannot be NULL!")
  }
  
  ## Read "homicides.txt" data file
  homicides <- readLines("homicides.txt")

  regex <- paste(" ", age, " year", sep = "")
  
  ## Extract ages of victims; ignore records where no age is given
  ## Return integer containing count of homicides for that age
  length(grep(regex, homicides))
}