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目标是在 for 循环中更改当前工作目录并在其中执行一些其他操作，例如搜索文件。路径存储在通用变量中。我为此运行的 R 代码如下：

require("foreach")

# The following lines are generated by an external tool and stored in filePath.info 
# Loaded via source("filePaths.info")
result1 <- '/home/user/folder1' 
result2 <- '/home/user/folder2'
result3 <- '/home/user/folder3' 
number_results <- 3

# So I know that I have all in all 3 folders with results by number_results 
# and that the variable name that contains the path to the results is generic: 
# string "result" plus 1:number_results.

# Now I want to switch to each result path and do some computation within each folder
start_dir <- getwd()
print(paste0("start_dir: ",start_dir))

# For every result folder switch into the directory of the folder
foreach(i=1:number_results) %do% { 
# for (i in 1:number_results){ leads to the same output

    # Assign path in variable, not the variable name as string: current_variable <- result1 (not string "result1")
    current_variable <- eval(parse(text = paste0("result", i)))
    print(paste0(current_variable, " in interation_", i))
    # Set working directory to string in variable current_variable
    current_dir <- setwd(current_variable)
    print(paste0("current_dir: ",current_dir))

    # DO SOME OTHER STUFF WITH FILES IN THE CURRENT FOLDER
}

# Switch back into original directory
current_dir <- setwd(start_dir)
print(paste0("end_dir: ",current_dir))

输出如下...

[1] "start_dir: /home/user"
[1] "/home/user/folder1 in interation_1"
[1] "current_dir: /home/user"
[1] "/home/user/folder2 in interation_2"
[1] "current_dir: /home/user/folder1"
[1] "/home/user/folder3 in interation_3"
[1] "current_dir: /home/user/folder2"
[1] "end_dir: /home/user/folder3"

...虽然我会预料到这一点：

[1] "start_dir: /home/user"
[1] "/home/user/folder1 in interation_1"
[1] "current_dir: /home/user/folder1"
[1] "/home/user/folder2 in interation_2"
[1] "current_dir: /home/user/folder2"
[1] "/home/user/folder3 in interation_3"
[1] "current_dir: /home/user/folder3"
[1] "end_dir: /home/user/"

所以事实证明，分配给 current_dir 的路径有点“落后”......

为什么会这样？由于我离成为 R 专家还很远，我不知道是什么导致了这种行为，最重要的是如何获得所需的行为。因此，我们将不胜感激任何帮助、提示、代码更正/优化！

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Platform: x86_64-pc-linux-gnu (64-bit)
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1 回答 1

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从?setwd帮助页面...

setwd返回更改前的当前目录，不可见且与getwd. 如果它不成功（包括如果它没有实现），它将给出一个错误。

所以当你这样做时

current_dir <- setwd(current_variable)
print(paste0("current_dir: ",current_dir))

您没有获得“当前”目录，而是获得了前一个目录。您应该使用getwd()来获取当前的

setwd(current_variable)
current_dir <- getwd()
print(paste0("current_dir: ",current_dir))
于 2016-09-16T15:48:09.130 回答