[英]Difference Between system() and system2() in R? Capture File Names in Variable
In R, I wanted to list files in a directory, and capture the output, but there were two calls to the system from R: system() and system2().在 R 中,我想列出目录中的文件,并捕获输出,但是 R 有两个对系统的调用:system() 和 system2()。 I was curious what the differences were, if any, and more importantly how to use them.我很好奇有什么区别,如果有的话,更重要的是如何使用它们。 There were some pages I found, includinghere and here , but I wanted to put some examples here, and the errors I encountered using system2(), including:我找到了一些页面,包括这里和这里,但我想在这里放一些例子,以及我在使用 system2() 时遇到的错误,包括:
sh: 1: ls /home : not found sh: 1: ls /home : 未找到
Prior to research, my first tries were all done in system()
, as I didn't know about system2()
.在研究之前,我的第一次尝试都是在system()
,因为我不知道system2()
。 I decided to redo my method in system2()
for portability (I'm working on a Linux system).我决定在system2()
重做我的方法以实现可移植性(我在 Linux 系统上工作)。 This led me to find a few differences.这让我发现了一些差异。
First, system()
solution to list files and save the output in a variable:首先, system()
解决方案列出文件并将输出保存在变量中:
gseaDirectory<-"/home"
filenames<-system(paste("ls", gseaDirectory, sep=" "), intern=T)
This stores a character string "/home", which is where my home directory is, into a variable gseaDirectory.这将我的主目录所在的字符串“/home”存储到变量 gseaDirectory 中。 I then was able to paste in the command ls
, a space, sep=" "
, and my directory variable gseaDirectory
into a linux command to list all files in the chosen directory:然后我能够将命令ls
、一个空格、 sep=" "
和我的目录变量gseaDirectory
到一个 linux 命令中,以列出所选目录中的所有文件:
ls /home
The list of files is then saved in the variable "filenames" with the added system() argument intern=T
.然后将文件列表保存在变量 "filenames" 中,并添加了 system() 参数intern=T
。
This doesn't work in system2(), and just returns the error:这在 system2() 中不起作用,只会返回错误:
sh: 1: ls /home : not found sh: 1: ls /home : 未找到
Our same method is changed slightly, with the equivalent system2()
command being:我们相同的方法略有变化,等效的system2()
命令是:
gseaDirectory<-"/home"
filenames<-system2('ls', paste(gseaDirectory, sep=" "), stdout = TRUE)
The first item in system2 is the command, then the target file, followed by stdout=T
which tells R we are going to store the output into a variable, otherwise the result of our command will be printed rather than saved. system2 中的第一项是命令,然后是目标文件,然后是stdout=T
,它告诉 R 我们将把输出存储到一个变量中,否则我们的命令的结果将被打印而不是保存。
Hope this helps someone!希望这可以帮助某人!
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