Include for loop iteration into a dataframe in R

Question

Very new to coding. I have been attempting to input values from a for loop iteration into a dataframe. I have looked at many asked questions however they did not seem to help my situation. Once my for loop is complete, my cat() outputs all values of the iteration. I have tried to create a dataframe using the names of the variables as you can see in the code however it only outputs one row with the last iteration. I have been told to create a dataframe before my for-loop in order to store the output values, but I cannot seem to figure it out. If anyone can show me the correct code that would be very greatly appreciated! Thank you

Numyears<- 0
NumLynxes<-0
NumHares<-0
flag<- F
NumBabyLynxes<-0
NumBabyHares<-0
NumDeadHares<-0
NumDeadLynxes<-0
NumHaresEaten<-0

while(flag !=T) {

ask <-readline(prompt = "Simulate the population of Lynx and Hares in Canada?
Type 1 for yes, Type anything else to exit:")
response<- as.integer(ask)

 if (response ==1) {
 variable1 <- readline(prompt = "Input the number of years for the simulation sample:")
 Numyears <- as.integer(variable1)
 variable2 <- readline(prompt="Enter the number of Lynxes in this simulation:")
 NumLynxes <- as.integer(variable2)
 variable3 <-readline("Enter the number of Hares in this simulation:")
 NumHares <-as.integer(variable3)

  DF <- data.frame(Numyears,NumHares,
                 NumLynxes,NumBabyHares,
                 NumBabyLynxes,
                 NumDeadHares,
                 NumDeadLynxes,
                 NumHaresEaten,stringsAsFactors = F)

  for (years in 1:Numyears) {

   if ( (NumLynxes/NumHares) < 0.20) {

    NumDeadLynxes<-round(NumLynxes * 0.02)
    NumBabyLynxes <- round(0.15*NumLynxes)
   }

   if ((NumLynxes/NumHares) >= 0.20) {
    NumDeadLynxes <- round(0.50*NumLynxes)
    NumBabyLynxes <- round(0.15*NumLynxes)
   }


   NumBabyHares<- round(0.75*NumHares)
   NumDeadHares <- round(NumDeadHares*0.01)
   NumHaresEaten <- round((NumLynxes*NumHares)*0.025)

   years <- years 
   NumLynxes <- ((NumLynxes + NumBabyLynxes) - NumDeadLynxes)
   NumHares <- ((NumHares + NumBabyHares) - (NumHaresEaten + NumDeadHares))

   if ((NumLynxes/NumHares) < 0){
    break
   }

   cat("Year  #Hares  #Lynxes  babyH  babyL  deadHare  deadLynx","\n",
      years," ","\t",NumHares," ","\t",NumLynxes, " ","\t",NumBabyHares, 
      " ","\t",NumBabyLynxes,"   ","\t",NumDeadHares," ","\t",NumDeadLynxes,
      " ", "\t",NumHaresEaten) 

  } 

 } else{
   flag <- T
 }
}
 DF

Answer 1

Look at this method instead.

1. I pre-allocate the entire DF with as many rows as needed. This prevents the "growing objects" problem referenced in chapter 2 of the R Inferno.

   I include the starting conditions in the data.frame. While not completely necessary, this makes calculation later on that much easier. Without it, we would need to calculate the next populations with if (row == 1) { calc_one_way; } else { calc_another_way; }, which seems easy enough but just reads poorly. If you don't like having the starting conditions in the first row, then you can always remove it at the very end with DF[-1,].

2. While we could technically use attach(DF) to prevent needing to reference DF$ every time, I strongly discourage it: it encourages some sloppy habits, and can and will cause problems at times if you are not very careful.

3. I'm inferring that we are growing (or eating) the population year-by-year, so we set next year's population based on this year's population and behavior. With that, I reference this year's numbers with [row] and set next year's numbers with [row+1]. Whenever indexing like that, care must be taken to never go too low ([0] is an error in R) or too high. In this case, since we have NumYears + 1 number of rows (I start with year 0 in row 1), and we only iterate from row 1 (year 0) to NumYears (nrow(DF) - 1), we're good with using [row] and [row+1] for row indices.

   Note: we start with row of 1 which reflects year 0 (starting conditions). That was my guess and is completely up to you.

flag <- FALSE

while(flag != TRUE) {

  ask <-readline(prompt = "Simulate the population of Lynx and Hares in Canada?
Type 1 for yes, Type anything else to exit:")
  response <- as.integer(ask)

  if (response == 1) {

    variable1 <- readline(prompt = "Input the number of years for the simulation sample:")
    NumYears <- as.integer(variable1)
    variable2 <- readline(prompt="Enter the number of Lynxes in this simulation:")
    NumLynxes <- as.integer(variable2)
    variable3 <- readline("Enter the number of Hares in this simulation:")
    NumHares <- as.integer(variable3)

    zeroes <- rep(0, NumYears + 1)
    DF <- data.frame(
      Year = c(0, seq_len(NumYears)),
      NumHares = c(NumHares, zeroes[-1]),
      NumLynxes = c(NumLynxes, zeroes[-1]),
      NumBabyHares = zeroes, NumBabyLynxes = zeroes,
      NumDeadHares = zeroes, NumDeadLynxes = zeroes,
      NumHaresEaten = zeroes)

    for (row in seq_len(NumRows)) {

      if ( (DF$NumLynxes[row] / DF$NumHares[row]) < 0.20) {
        DF$NumDeadLynxes[row + 1] <- round(DF$NumLynxes[row] * 0.02)
        DF$NumBabyLynxes[row + 1] <- round(0.15 * DF$NumLynxes[row])
      } else {
        DF$NumDeadLynxes[row + 1] <- round(0.50 * DF$NumLynxes[row])
        DF$NumBabyLynxes[row + 1] <- round(0.15 * DF$NumLynxes[row])
      }


      DF$NumBabyHares[row] <- round(0.75 * DF$NumHares[row])
      DF$NumDeadHares[row] <- round(DF$NumDeadHares[row] * 0.01)
      DF$NumHaresEaten[row] <- round((DF$NumLynxes[row] * DF$NumHares[row]) * 0.025)

      DF$NumLynxes[row + 1] <- ((DF$NumLynxes[row] + DF$NumBabyLynxes[row]) - DF$NumDeadLynxes[row])
      DF$NumHares[row + 1] <- ((DF$NumHares[row] + DF$NumBabyHares[row]) - (DF$NumHaresEaten[row] + DF$NumDeadHares[row]))

      if (DF$NumLynxes[row] <= 0) {
        break
      }

      print(DF[row + 1,])

    }

  } else{
    flag <- TRUE
  }
}

In the end, there might be other things going on: when I start with 10 of each Hares/Lynxes, then the growth is a little explosive ...

DF
#    Year NumHares NumLynxes NumBabyHares NumBabyLynxes NumDeadHares NumDeadLynxes NumHaresEaten
# 1     0       10        10            8             0            0             0             2
# 2     1       16        10           12             2            0             5             4
# 3     2       24         7           18             2            0             5             4
# 4     3       38         4           28             1            0             4             4
# 5     4       62         1           46             1            0             0             2
# 6     5      106         2           80             0            0             0             5
# 7     6      181         2          136             0            0             0             9
# 8     7      308         2          231             0            0             0            15
# 9     8      524         2          393             0            0             0            26
# 10    9      891         2          668             0            0             0            45
# 11   10     1514         2         1136             0            0             0            76
# 12   11     2574         2         1930             0            0             0           129
# 13   12     4375         2         3281             0            0             0           219
# 14   13     7437         2         5578             0            0             0           372
# 15   14    12643         2         9482             0            0             0           632
# 16   15    21493         2        16120             0            0             0          1075
# 17   16    36538         2        27404             0            0             0          1827
# 18   17    62115         2        46586             0            0             0          3106
# 19   18   105595         2        79196             0            0             0          5280
# 20   19   179511         2       134633             0            0             0          8976
# 21   20   305168         2            0             0            0             0             0

Have fun.