blocks|key|55040|text|如果希望程序产生错误，可以使用stopifnot()函数：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|55041|foo+<-+function(x)+{
++++stopifnot(x+>+500)
++++#+rest+of+program
}|code-block|syntax|javascript|55042|entityMap^0|F|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You could use the <code>stopifnot()</code> function if you want the program to produce an error:

<pre><code>foo &lt;- function(x) {
 stopifnot(x &gt; 500)
 # rest of program
}
</code></pre>

blocks|key|55210|text|也许你只是想在某个时刻停止执行一个长脚本。即。就像你想用C或Python硬编码一个exit()一样。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|55211|print("this+is+the+last+message")
stop()
print("you+should+not+see+this")|code-block|syntax|javascript|55212|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Perhaps you just want to stop executing a long script at some point. ie. like you want to hard code an exit() in C or Python.

<pre><code>print("this is the last message")
stop()
print("you should not see this")
</code></pre>

blocks|key|271455|text|反转if-else结构：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|271456|if(n+>=+500)+{
++#+do+stuff
}
#+no+need+for+else|code-block|syntax|javascript|271457|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Reverse your if-else construction:

<pre><code>if(n &gt;= 500) {
 # do stuff
}
# no need for else
</code></pre>

blocks|key|55293|text|这是一个古老的问题，但目前还没有一个干净的解决方案。这可能不是在回答这个特定的问题，但是那些正在寻找“如何优雅地退出R脚本”的人可能会在这里找到答案。R开发人员似乎忘记了实现exit()函数。不管怎样，我发现的诀窍是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|55294|continue+<-+TRUE

tryCatch({
+++++#+You+do+something+here+that+needs+to+exit+gracefully+without+error.
+++++...

+++++#+We+now+say+bye-bye+++++++++
+++++stop("exit")

},+error+=+function(e)+{
++++if+(e$message+!=+"exit")+{
++++++++#+Your+error+message+goes+here.+E.g.
++++++++stop(e)
++++}

++++continue+<<-FALSE
})

if+(continue)+{
+++++#+Your+code+continues+here
+++++...
}

cat("done.\n")|code-block|syntax|javascript|55295|基本上，您使用一个标志来指示指定代码块是否继续。然后使用stop()函数向tryCatch()函数的错误处理程序传递一条定制的消息。如果错误处理程序接收到要正常退出的消息，那么它将忽略该错误，并将继续标志设置为FALSE。|offset|length|style|CODE|55296|entityMap^0|0|0|S|6|11|A|2X|5|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]|$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|N|$]]

This is an old question but there is no a clean solution yet. This probably is not answering this specific question, but those looking for answers on 'how to gracefully exit from an R script' will probably land here. It seems that R developers forgot to implement an exit() function. Anyway, the trick I've found is:

<pre><code>continue &lt;- TRUE

tryCatch({
 # You do something here that needs to exit gracefully without error.
 ...

 # We now say bye-bye 
 stop("exit")

}, error = function(e) {
 if (e$message != "exit") {
 # Your error message goes here. E.g.
 stop(e)
 }

 continue &lt;&lt;-FALSE
})

if (continue) {
 # Your code continues here
 ...
}

cat("done.\n")
</code></pre>

Basically, you use a flag to indicate the continuation or not of a specified block of code. Then you use the <code>stop()</code> function to pass a customized message to the error handler of a <code>tryCatch()</code> function. If the error handler receives your message to exit gracefully, then it just ignores the error and set the continuation flag to <code>FALSE</code>.

blocks|key|55080|text|这里：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|55081|if(n+<+500)
{
++++#+quit()
++++#+or+
++++#+stop("this+is+some+message")
}
else
{
++++*insert+rest+of+program+here*
}|code-block|syntax|javascript|55082|quit()和stop(message)都会退出你的脚本。如果您从R命令提示符获取脚本，那么quit()也将从R退出。|offset|length|style|CODE|55083|entityMap^0|0|0|0|6|7|D|1A|6|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]|$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|N|$]]

Here:

<pre><code>if(n &lt; 500)
{
 # quit()
 # or 
 # stop("this is some message")
}
else
{
 *insert rest of program here*
}
</code></pre>

Both <code>quit()</code> and <code>stop(message)</code> will quit your script. If you are sourcing your script from the R command prompt, then <code>quit()</code> will exit from R as well.

blocks|key|271770|text|我有一个类似的问题:退出当前函数，但不想完成其余的代码。最后，我通过一个只运行一次的for()循环解决了这个问题。在for循环中，您可以设置几个不同的条件来离开当前循环(函数)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|271771|++for+(i+in+T)+{
++++print('hello')
++++if+(leave.condition)+next
++++print('good+bye')
++}|code-block|syntax|javascript|271772|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I had a similar issue: Exit the current function, but not wanted to finish the rest of the code.
Finally I solved it by a for() loop that runs only once. Inside the for loop you can set several differenct conditions to leave the current loop (function).
<pre><code> for (i in T) {
 print('hello')
 if (leave.condition) next
 print('good bye')
 }
</code></pre>

blocks|key|55156|text|您可以使用R的tools包中的pskill函数来中断当前进程并返回控制台。具体地说，我在每个脚本开头的启动文件中定义了以下函数。但是，您也可以直接在代码的开头复制它。然后在代码中的任意位置插入halt()以动态停止脚本执行。这个函数在GNU/Linux上工作得很好，从R文档来看，它也应该可以在Windows上工作(但我没有检查)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|55157|#+halt:+interrupts+the+current+R+process;+a+short+iddle+time+prevents+R+from
#+outputting+further+results+before+the+SIGINT+(=+Ctrl-C)+signal+is+received+
halt+<-+function(hint+=+"Process+stopped.\n")+{
++++writeLines(hint)
++++require(tools,+quietly+=+TRUE)
++++processId+<-+Sys.getpid()+
++++pskill(processId,+SIGINT)
++++iddleTime+<-+1.00
++++Sys.sleep(iddleTime)
}|code-block|syntax|javascript|55158|entityMap^0|5|1|F|6|2O|6|3Q|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|L|$]]

You can use the <code>pskill</code> function in the <code>R</code> "tools" package to interrupt the current process and return to the console. Concretely, I have the following function defined in a startup file that I source at the beginning of each script. You can also copy it directly at the start of your code, however. Then insert <code>halt()</code> at any point in your code to stop script execution on the fly. This function works well on GNU/Linux and judging from the <code>R</code> documentation, it should also work on Windows (but I didn't check).

<pre><code># halt: interrupts the current R process; a short iddle time prevents R from
# outputting further results before the SIGINT (= Ctrl-C) signal is received 
halt &lt;- function(hint = "Process stopped.\n") {
 writeLines(hint)
 require(tools, quietly = TRUE)
 processId &lt;- Sys.getpid() 
 pskill(processId, SIGINT)
 iddleTime &lt;- 1.00
 Sys.sleep(iddleTime)
}
</code></pre>

I have a program that does some data analysis and is a few hundred lines long. 

Very early on in the program, I want to do some quality control and if there is not enough data, I want the program to terminate and return to the R console. Otherwise, I want the rest of the code to execute.

I've tried <code>break</code>,<code>browser</code>, and <code>quit</code> and none of them stop the execution of the rest of the program (and <code>quit</code> stops the execution as well as completely quitting R, which is not something I want to happen). My last resort is creating an <code>if-else</code> statement as below:

<pre><code> if(n &lt; 500){}
 else{*insert rest of program here*}
</code></pre>

but that seems like bad coding practice. Am I missing something?

break/exit script

数据分析

Windows

Python

Linux

我有一个程序，它做一些数据分析，有几百行代码。在程序的早期，我想做一些质量控制，如果没有足够的数据，我希望程序终止并返回R控制台。否则，我希望执行其余的代码。我尝试过break、browser和quit，但它们都没有停止程序其余部分的执行( quit会停止执行并完全退出R，这不是我想要发生的事情)。我最后的办法是创建一条if-else语句，如下所示： if(n < 500){} else{*ins

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