理解R中的这个Collat​​z功能代码

Question

我是R编程语言的新手并且想为这种简单的问题感到抱歉并且已经在R中解密了collat​​z猜想的代码。实际上，我已经完全理解了前两部分，但我没有逻辑第3部分中的while循环以及n.total＆lt; - NULL的需要。另外，我不明白为什么它将整个集合作为最后一步中的向量与c（n.total，n）组合的原因。非常感谢你的帮助！

Part 1:

is.even <- function(x){
  if(x%%2==0){
    print("TRUE")
  }else{
    print("FALSE")
  }
}

Part 2:

collatz <- function(n){
  if (is.even(n)) {
    n/2
  }else{
      3*n+1
    }
}

Part 3:

n <- 27
n.total <- NULL
while(n != 1){
  n <- collatz(n)
  n.total <- c(n.total,n)
}

n.total

Answer 1

collatz <- function(n, acc=c()) {
  if(n==1) return(c(acc, 1));
  collatz(ifelse(n%%2==0, n/2, 3*n +1), c(acc, n))} 

collat​​z（5）将返回：5 16 8 4 2 1

Answer 2

is.even() should return its result, not print it, which is breaking things. You can just use a direct logical expression for is.even():

is.even <- function(x) { x%%2==0 }

But it's so short you can inline it, no need for a function call. Also, prefer ifelse expressions to if...else ladders of assignments/expressions.

collatz <- function(n) { ifelse(n%%2==0, n/2, 3*n +1 }