R - Middle Square Method

gistfile1.txt

# seed requires an even length number, no restrictions on length
# number is the number of numbers you wish to be generated
# raw=1 returns raw data, aka "0429" instead of 429
# this method is horrible, but still often used as a teaching method 

MSM <- function(seed, number, raw) {
  options("scipen" = 2*nchar(seed))
  
  if(missing(number)) {
    number <- 15
  }
  
  if(missing(raw)) {
    raw <- 1
  }
  
  if(nchar(seed)%%2 != 0){
    cat("Please enter a seed with an even number of digits")
    cat("\n")
    stop
  } else  
  while_char <- seed
  library(stringi)
  MSM_LIST <- c()
  for(i in 1:number){
    seed_sqr <- seed^2
    
    #this while loop adds trailing zeros
    while(nchar(seed_sqr) < 2*nchar(while_char)) {
      seed_sqr<- stri_pad_left(seed_sqr, 2*nchar(while_char), 0)
    }
    
    
    
    #this section identifies the middle number
    left_digit <- nchar(seed_sqr)/4 + 1
    right_digit <- nchar(seed_sqr) - (nchar(seed_sqr)/4)
    ran_num <- as.numeric(substr(seed_sqr, left_digit, right_digit))
    
    while(nchar(ran_num) < nchar(while_char)){
      ran_num <- stri_pad_left(ran_num, nchar(while_char), 0)
    }
    
    MSM_LIST[i] <- ran_num 
    ran_num <- as.numeric(ran_num)
    seed <- ran_num
    while_char <- substr(seed_sqr, left_digit, right_digit) 
  }
  
  ifelse(raw==1, MSM_LIST,
         ifelse(raw==0, MSM_LIST <- as.numeric(MSM_LIST))
  )
  MSM_LIST
}