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1: R Programming
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1: Basic Building Blocks 2: Workspace and Files 3: Sequences of Numbers
4: Vectors 5: Missing Values 6: Subsetting Vectors
7: Matrices and Data Frames 8: Logic 9: Functions
10: lapply and sapply 11: vapply and tapply 12: Looking at Data
13: Simulation 14: Dates and Times 15: Base Graphics
Selection: 2
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| In this lesson, you'll learn how to examine your local workspace in R and begin to explore
| the relationship between your workspace and the file system of your machine.
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|== | 2%
| Because different operating systems have different conventions with regards to things like
| file paths, the outputs of these commands may vary across machines.
...
|==== | 5%
| However it's important to note that R provides a common API (a common set of commands) for
| interacting with files, that way your code will work across different kinds of computers.
...
|====== | 7%
| Let's jump right in so you can get a feel for how these special functions work!
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|======== | 10%
| Determine which directory your R session is using as its current working directory using
| getwd().
> getwd()
[1] "/Users/xiaomodepro/DataAnalysis"
| Keep up the great work!
|========== | 12%
| List all the objects in your local workspace using ls().
> ls()
character(0)
| You are quite good my friend!
|============= | 15%
| Some R commands are the same as their equivalents commands on Linux or on a Mac. Both
| Linux and Mac operating systems are based on an operating system called Unix. It's always
| a good idea to learn more about Unix!
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|=============== | 17%
| Assign 9 to x using x <- 9.
> x<-9
| You are really on a roll!
|================= | 20%
| Now take a look at objects that are in your workspace using ls().
> ls()
[1] "x"
| Keep working like that and you'll get there!
|=================== | 22%
| List all the files in your working directory using list.files() or dir().
> list.files()
[1] "Anscombe.R" "case_Anscombe.R"
| Nice work!
|===================== | 24%
| As we go through this lesson, you should be examining the help page for each new function.
| Check out the help page for list.files with the command ?list.files.
> ?list.files
| Keep working like that and you'll get there!
|======================= | 27%
| One of the most helpful parts of any R help file is the See Also section. Read that
| section for list.files. Some of these functions may be used in later portions of this
| lesson.
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|========================= | 29%
| Using the args() function on a function name is also a handy way to see what arguments a
| function can take.
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|=========================== | 32%
| Use the args() function to determine the arguments to list.files().
> args(list.files)
function (path = ".", pattern = NULL, all.files = FALSE, full.names = FALSE,
recursive = FALSE, ignore.case = FALSE, include.dirs = FALSE,
no.. = FALSE)
NULL
| You got it right!
|============================= | 34%
| Assign the value of the current working directory to a variable called "old.dir".
> old.dir<-getwd()
| You're the best!
|=============================== | 37%
| We will use old.dir at the end of this lesson to move back to the place that we started. A
| lot of query functions like getwd() have the useful property that they return the answer
| to the question as a result of the function.
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|================================== | 39%
| Use dir.create() to create a directory in the current working directory called "testdir".
> dir.create("testdir")
| Excellent job!
|==================================== | 41%
| We will do all our work in this new directory and then delete it after we are done. This
| is the R analog to "Take only pictures, leave only footprints."
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|====================================== | 44%
| Set your working directory to "testdir" with the setwd() command.
> setwd("testdir")
| Excellent job!
|======================================== | 46%
| In general, you will want your working directory to be someplace sensible, perhaps created
| for the specific project that you are working on. In fact, organizing your work in R
| packages using RStudio is an excellent option. Check out RStudio at
| http://www.rstudio.com/
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|========================================== | 49%
| Create a file in your working directory called "mytest.R" using the file.create()
| function.
> file.create("mytest.R")
[1] TRUE
| You got it!
|============================================ | 51%
| This should be the only file in this newly created directory. Let's check this by listing
| all the files in the current directory.
> list.files()
[1] "mytest.R"
| Nice work!
|============================================== | 54%
| Check to see if "mytest.R" exists in the working directory using the file.exists()
| function.
> file.exists("mytest.R")
[1] TRUE
| All that hard work is paying off!
|================================================ | 56%
| These sorts of functions are excessive for interactive use. But, if you are running a
| program that loops through a series of files and does some processing on each one, you
| will want to check to see that each exists before you try to process it.
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|================================================== | 59%
| Access information about the file "mytest.R" by using file.info().
> file.info("mytest.R")
size isdir mode mtime ctime atime uid gid
mytest.R 0 FALSE 644 2015-05-08 00:36:33 2015-05-08 00:36:33 2015-05-08 00:36:33 501 20
uname grname
mytest.R xmuxiaomo staff
| That's the answer I was looking for.
|==================================================== | 61%
| You can use the $ operator
| items.
...
|======================================================= | 63%
| Change the name of the file "mytest.R" to "mytest2.R" by using file.rename().
> file.rename("mytest.R","mytest2.R")
[1] TRUE
| You got it right!
|========================================================= | 66%
| Your operating system will provide simpler tools for these sorts of tasks, but having the
| ability to manipulate files programatically is useful. You might now try to delete
| mytest.R using file.remove('mytest.R'), but that won't work since mytest.R no longer
| exists. You have already renamed it.
...
|=========================================================== | 68%
| Make a copy of "mytest2.R" called "mytest3.R" using file.copy().
> file.copy("mytest2.R","mytest3.R")
[1] TRUE
| That's the answer I was looking for.
|============================================================= | 71%
| You now have two files in the current directory. That may not seem very interesting. But
| what if you were working with dozens, or millions, of individual files? In that case,
| being able to programatically act on many files would be absolutely necessary. Don't
| forget that you can, temporarily, leave the lesson by typing play() and then return by
| typing nxt().
...
|=============================================================== | 73%
| Provide the relative path to the file "mytest3.R" by using file.path().
> file.path("mytest3.R")
[1] "mytest3.R"
| Perseverance, that's the answer.
|================================================================= | 76%
| You can use file.path to construct file and directory paths that are independent of the
| operating system your R code is running on. Pass 'folder1' and 'folder2' as arguments to
| file.path to make a platform-independent pathname.
> file.path("folder1","folder2")
[1] "folder1/folder2"
| All that practice is paying off!
|=================================================================== | 78%
| Take a look at the documentation for dir.create by entering ?dir.create . Notice the
| 'recursive' argument. In order to create nested directories, 'recursive' must be set to
| TRUE.
> ?dir.create
| You are amazing!
|===================================================================== | 80%
| Create a directory in the current working directory called "testdir2" and a subdirectory
| for it called "testdir3", all in one command by using dir.create() and file.path().
> dir.create(file.path("testdir2","testdir3"),recursive=TRUE)
| Excellent job!
|======================================================================= | 83%
| To delete a directory you need to use the recursive = TRUE argument with the function
| unlink(). If you don't use recursive = TRUE, R is concerned that you're unaware that
| you're deleting a directory and all of its contents. R reasons that, if you don't specify
| that recursive equals TRUE, you don't know that something is in the directory you're
| trying to delete. R tries to prevent you from making a mistake.
...
|========================================================================= | 85%
| Delete the "testdir2" directory that you created by using unlink().
> unlink("testdir2",recursive=TRUE)
| You got it!
|============================================================================ | 88%
| Why is this command named "unlink" rather than something more sensible like "dir.delete"
| or "dir.remove"? Mainly, history. unlink is the traditional Unix command for removing
| directories.
...
|============================================================================== | 90%
| Go back to your original working directory using setwd(). (Recall that we created the
| variable old.dir with the full path for the orginal working directory at the start of
| these questions.)
> setwd(old.dir)
| Keep up the great work!
|================================================================================ | 93%
| It is often helpful to save the settings that you had before you began an analysis and
| then go back to them at the end. This trick is often used within functions; you save, say,
| the par() settings that you started with, mess around a bunch, and then set them back to
| the original values at the end. This isn't the same as what we have done here, but it
| seems similar enough to mention.
...
|================================================================================== | 95%
| Delete the 'testdir' directory that you just left (and everything in it)
> unlink("testdir",recursive=TRUE)
| That's a job well done!
|==================================================================================== | 98%
| Take nothing but results. Leave nothing but assumptions. That sounds like 'Take nothing
| but pictures. Leave nothing but footprints.' But it makes no sense! Surely our readers can
| come up with a better motto . . .
...
|======================================================================================| 100%
| In this lesson, you learned how to examine your R workspace and work with the file system
| of your machine from within R. Thanks for playing!
...
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