Length of r array-CodePudding

I try to return the Y array from the second loop. I expect it to be (n - [k 2]) length but I get output of n length array

a1q1 <- function (n , j , k , m, X0) {
  X <- numeric(length=n)
  Xn <- X0
  for (i in 1:n) {
    Xn <- (103515245*Xn   12345) %% 2^32
    X[i] <- Xn
  }
  Y <- numeric(length=n - k - 1)
  for (i in k   2:n) {
    Y[i - k - 1] <- (X[i - j]   X[i - k]) %% m
  }
  return (Y)
}

Z <- a1q1(100, 5, 90, 11, 0)
Z
# [1]  6  5  8  3  1 10  1  1  9  6  2  2  5  7 NA NA NA NA NA NA NA NA NA NA NA NA
# [27] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
# [53] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
# [79] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA

CodePudding user response：

This often catches me too. You need to put parentheses around k 2, in the second for loop.. Try this minor adjustment below:

  for (i in (k 2):n) {
    Y[i-k-1] <- (X[i-j]   X[i-k]) %% m
  }

CodePudding user response：

@langtang has shown what you need to do.

The problem is operator precedence:

> 1 2:3
[1] 3 4
> (1 2):3
[1] 3

It is often a good idea to use parenthesis to avoid things like this, and it makes the code easier to read.