R重复功能直到满足条件 [英] R repeat function until condition met

问题描述

我正在尝试生成排除某些不良数据"的随机样本.我不知道数据是否坏"，直到我采样之后.因此，我需要从人群中随机抽取，然后进行测试.如果数据好"，则保留它.如果数据不好"，则随机抽取另一个数据并进行测试.我想这样做，直到我的样本量达到 25.下面是我尝试编写一个执行此操作的函数的简化示例.谁能告诉我我错过了什么?

I am trying to generate a random sample that excludes certain "bad data." I do not know whether the data is "bad" until after I sample it. Thus, I need to make a random draw from the population and then test it. If the data is "good" then keep it. If the data is "bad" then randomly draw another and test it. I would like to do this until my sample size reaches 25. Below is a simplified example of my attempt to write a function that does this. Can anyone please tell me what I am missing?

df <- data.frame(NAME=c(rep('Frank',10),rep('Mary',10)), SCORE=rnorm(20))
df

random.sample <- function(x) {
  x <- df[sample(nrow(df), 1), ]
  if (x$SCORE > 0) return(x)
 #if (x$SCORE <= 0) run the function again
}

random.sample(df)

推荐答案

下面是 while 循环的一般用法:

Here is a general use of a while loop:

random.sample <- function(x) {
  success <- FALSE
  while (!success) {
    # do something
    i <- sample(nrow(df), 1)
    x <- df[sample(nrow(df), 1), ]
    # check for success
    success <- x$SCORE > 0
  }
  return(x)
}

另一种方法是使用 repeat(while(TRUE) 的语法糖)和 break:

An alternative is to use repeat (syntactic sugar for while(TRUE)) and break:

random.sample <- function(x) {
  repeat {
    # do something
    i <- sample(nrow(df), 1)
    x <- df[sample(nrow(df), 1), ]
    # exit if the condition is met
    if (x$SCORE > 0) break
  }
  return(x)
}

其中 break 使您退出 repeat 块.或者，您可以让 if (x$SCORE > 0) return(x) 直接退出函数.

where break makes you exit the repeat block. Alternatively, you could have if (x$SCORE > 0) return(x) to exit the function directly.

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