r - 为什么我的 for 循环在 R 中运行一次额外的迭代？

Question

我试图在 R 中运行以下简单代码，但 for 循环运行一次额外的迭代，我无法弄清楚其背后的原因。你能帮我吗？

fun <- function(x) { 
  y <- as.character(0)
  for (i in 1:length(x)) {
    if (x[i] == "NO") {
      y[i] <- c("Its a NO")
      y <- append(y, y[i])
    } else if (x[i] == "YES") {
      y[i] <- c("Its a YES")
      y <- append(y, y[i])
    } else {
      y[i] <- c("Don't know")
      y <- append(y, y[i])      
    }    
  }
  return(y)
}

a <- c("YES","NA", "NO")

fun(a)

提前非常感谢。

Answer 1

一种选择是将“y”初始化为“x”的长度，然后删除append

fun <- function(x) { 
  y <- character(length(x))
  for (i in seq_along(x)) {
    y[i] <- if (x[i] == "NO") {
      c("Its a NO")  
    } else if (x[i] == "YES") {
      c("Its a YES")        
    } else {
      c("Don't know")
    }
  }
  return(y)
}

a <- c("YES","NA", "NO")

fun(a)
#[1] "Its a YES"  "Don't know" "Its a NO"