在 R 程序中要求用户输入的正确方法是什么?

问题描述：

如果我分别运行下面的程序(分为两部分)，它们就可以工作——也就是说，如果我将第一部分粘贴到 R 控制台中，运行它，然后粘贴第二部分并运行它.然而，这不是我想要的.我想一次运行整个程序.如果我这样做，它会在我的控制台中显示以下错误:

The my program below(which is in two parts) works if I run them separately – that is, if I paste the first part into the R Console, run it and then paste the second and run it. However, that is not how I want it. I want to run the whole program at once. If I do that it shows the following error in my console :

1: 
Read 0 items
1: 
Read 0 items
Error in while ((n <= 0) | (acr <= 0) | (acr >= 1)) { : 
  argument is of length zero

我已尝试确定问题，但无法找到根本原因.如果有人可以帮助我，我会非常高兴.

I have tried to identify the problem but I have not been able find the root cause. I would be more than glad, if someone could come to my aid.

#**FIRST PART OF THE PROGRAM**

n <- -2
acr <- -2
while((n<=0) | (acr<=0) | (acr>=1)) {
   print("enter a  positive integer and the average cancellation rate between 0 and 1  
                you want")
   try(n <- scan(what=integer(), nmax=1), silent=TRUE)
   try(acr <- scan(what=double(), nmax=1), silent=TRUE)
}


#**SECOND PART OF THE PROGRAM**

bygrace <- read.table("C:\\MyRfolder\\bygrace.txt", header=FALSE)
r <- nrow(bygrace)
c <- ncol(bygrace)
copybygrace <- array(bygrace, dim=c(r, c))
copybygrace <- bygrace[-((n+1):r), ]
write.table(copybygrace,file="C:\\MyRfolder\\copybygrace.txt", sep="\t")
copybygrace <- read.table("C:\\MyRfolder\\copybygrace.txt", header=TRUE)

答

@Marek 说得很对.补充几点:

@Marek is very right. A few more remarks :

一般来说，你不应该使用 scan() 而应该使用 readline() .
我会拆分代码，以便清楚哪些内容适合在 n 中读取，哪些内容适合在 acr 中读取.
想想您是想在人们按 Enter 键时返回提示，还是想重新提问直到他们填写正确的值.
您可以使用 grepl() 的强大功能来检查输入的格式是否正确.

In general, you shouldn't be using scan() but readline() for this.
I'd split the code so it becomes clear what serves to read in n, and what serves to read in acr.
think about whether you want to return to the prompt when people just press enter, or whether you want to reask the question until they fill in some correct value.
you can use the power of grepl() to check whether the input is the right format.

为了包含正确的控件并捕获所有可能的错误，以下构造更加简洁，并且在复制到控制台时不会破坏您的代码:

To include the correct controls and catch all possible mistakes, the following construct is a lot cleaner and won't break your code when copied to the console :

while(n < 1 ){
  n <- readline("enter a positive integer: ")
  n <- ifelse(grepl("\\D",n),-1,as.integer(n))
  if(is.na(n)){break}  # breaks when hit enter
}

这显示了当人们不填写任何内容时如何终止问题.grepl 构造排除了任何不是数字的字符，包括点.

This shows how to terminate the question when people don't fill in anything. The grepl construct exludes any character that is not a digit, including the dot.

while(is.na(acr) | acr <= 0 | acr >= 1 ){
  acr <- readline("and the average cancellation rate between 0 and 1 :")
  acr <- ifelse(grepl("[^0-9.]",acr),-1,as.numeric(acr))
}

这显示了当人们没有填写任何内容时如何重新提问.grepl 排除任何不是数字或点的字符.

This shows how to re-ask the question when people don't fill in anything. The grepl excludes any character that is not a digit or a dot.

在 R 程序中要求用户输入的正确方法是什么?

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