在R程序中请求用户输入的正确方法是什么?

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 :

下面的my程序(分为两部分)如果我单独运行它们，也就是说，如果我将第一部分粘贴到R控制台，运行它，然后粘贴第二个并运行它。然而，这不是我想要的。我想立刻运行整个程序。如果我这样做，它会在我的控制台中显示以下错误:

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

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.

我已设法查明问题的症结所在，但没有找到根本原因。如果有人能来帮助我，我会非常高兴。

#**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)

2 个解决方案

#1

@Marek is very right. A few more remarks :

@Marek是非常正确的。再说几句话:

In general, you shouldn't be using scan() but readline() for this.
一般来说，您不应该为此使用scan()而应该使用readline()。
I'd split the code so it becomes clear what serves to read in n, and what serves to read in acr.
我将代码拆分，这样就可以清楚地知道在n中读什么，以及在acr中读什么。
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.
考虑当人们按下enter时，您是否希望返回到提示符，或者您是否希望重新分配问题，直到他们填入一些正确的值。
you can use the power of grepl() to check whether the input is the right format.
您可以使用grepl()的功能检查输入是否是正确的格式。

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 :

为了包含正确的控件并捕获所有可能的错误，下面的构造要干净得多，并且在复制到控制台时不会破坏代码:

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
}

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.

这说明了当人们什么都不填时，如何终止这个问题。grepl构造会删除任何非数字的字符，包括点。

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))
}

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.

这展示了当人们什么都不填的时候如何重新问问题。grepl排除任何不是数字或点的字符。

#2

It's because when you copy and paste all then scan reads pasted lines as input.

这是因为当你复制和粘贴所有，然后扫描读取粘贴行作为输入。

If you copy this tree lines to console

如果将此树行复制到控制台

x <- scan(nmax=1)
1
2

x become 1, scan don't wait for your interaction cause it got line to read.

x变成1，扫描不要等待你的交互作用，因为它有行读。

You have to wrap everything in {}:

你必须把所有东西都包装在{}:

{
 x <- scan(nmax=1)
 1
 2
}

You have to wrap both parts of your program. To be more clear: when you paste your code to console } should be last sign.

你必须把程序的两个部分都打包。更清楚的是:当您将代码粘贴到控制台}时，应该是最后一个符号。

#1