I'm going to talk about two things in this video. The first thing is how to set your working directory. And the second thing is how to edit R code files using the text editor. So, when you start up R you, it's important to know what your working directory is. Because the working directory is where R reads and write files to the computer. And if you don't know where that directory is, then you're not going to be able to, find any of the files that you save, or any of the data that you write out. So when you start up R, you can find out what your working directory is by just typing the function getwd. And you can see that I've loaded up R here and it, and it sets my working directory to be /Users/rdpeng, which on the Mac is just your home directory. So this may work but in, if you store all your files in your home directory but you may want to change your working directory to be something else if happen to store all of your data and code files in a different directory maybe a sub directory. So for example I can go to the Misc menu here and just hit, and choose Change Working Directory. And I can choose one of these directories to be my working directory. Now before I go, the first thing I want to mention actually is, that if you want to read a file, then that file has to be in your working directory, otherwise you'll get an error. So for example, suppose I want to read a data file using read.csv and I want to read the mydata.csv file, okay? So if this file is in my working directory then I'll be able to read the data, and it will load it into R. But if it's not, I'll get an error like this, because the file can't be found in my working directory. So one thing I could do is I can change my working directory to be, to be wherever that file happens to be. So I'll choose the class directory here. And if I type dir in this directory, it'll list all the files in this directory. And now you can see, oh mydata.csv is in this directory. So I'm going to, now I can read the file into R by typ, using read.csv and now you'll see that the data will appear in R. So so knowing what your working directory is and being able to set it is important because then you'll, it'll give you, it will give you access to all the files that you need in R. In particular, when you save files say from the web on to your computer, you need to know where those files are stored on your computer and so that you can set your working directory to the appropriate place. Or you can move those files into your working directory. I recommend for this class that you, that you create a specific directory for this class and store all the files in that class. That way you don't have to worry about changing directories all the time. One thing you can do is maybe just create a directory right here on your desktop, so I'm going to create a directory here called Coursera. And now, when I'm in R, I can say Change Direc, Change Working Directory here. And if I go to my desktop I can choose my Coursera folder there. And now, when I, when I say getwd, you'll see that it has set the working directory to be my Coursera folder. So now if you save files in there, you, they will be there, then you can, and you can read them from R. So that may be the be, the easiest thing for one to do. So the one thing that you're going to have to do a lot of in this course is to write code in R, and to, and you're going to need an editor to do that. So one nice thing about R on the Mac is that it comes with a text editor that you can use to edit code files. So I can load up the text editor by clicking on this little button right here. And this gives me an empty file. So I'm going to move this over here. And you can start editing code right away. So I can say, I can create a myfunctions, so call it myfunctions, and I can, it, it will start indenting things. So I can say, you know, x is, rnorm, 100. And this function, is going to just take the mean of x here. So, actually, let me just change this to y. And, and it just returns the mean. So it ignores the argument for now. So, and then, and then one thing you're going to have to do is, is figure out how to get this code into R. So what you'll notice, if I just type my function here, it's not going to be able to find it because the code has not been loaded into R. If I type ls, you'll see that there are no objects in my work space. So, the question is, how do I get this code that I've written over here, into R? Well, the easiest thing you can do, if you just have a little bit of the code, is just to hit Select All, so this is Cmd+A. Or you can go to the Edit menu and just hit Select All. And then Cmd+C copies the code and then I can click into my console window over here, hit a Cmd+V and and then return and it will paste my function into R. So now if I type ls you'll see that my function is an object in my workspace. So I can say myfunction. And it will return the mean of a hundred random normal variables, which is not very interesting, but the function does work. So the other thing you can do is you can save this file. I can go to the File menu and I want to Save As. So I haven't saved this file before, so I need to Save As. And I'm going to go into my Coursera folder and I'm, I'm going to save it as myfunction and it is typical to add the .r extension for code files. And I can hit Save. And so now, I want, I can double check my working directory, and make sure I'm in the right place here. Yeah, I'm in the Coursera, working directory. If I type dir, you'll see that my, the myfunction.r file is there now. So I can just source the file, myfunction.r. And it will have the same, it will have the same effect as cutting and pasting. So I, so I haven't done anything new because I already cut and pasted that function. But one thing I can do, I can write, I can write another function here so, say, I'll call it second to indicate it's the second function, and it's going to take the input x, oop, excuse me. And it's going to add a little bit of noise to it. And that's all it's going to do. It's going to return that. So so what, now before I do anything, I need to, now that I've changed the file, I need to save it. So I can just go to File > Save, or you can do Cmd+S. And now I can source my, this, this file into R again. And you'll notice I type ls, I got a, I have my second function there. So if I type this out, you'll see that's the code for it. So now I'll say second I say four and I return four plus a little bit of noise. If I do it again, it'll be four plus a little bit of more noise. I can give it four through ten and it gives me each one of those numbers with a little bit of noise. So that's how I write code in R. And that's how I can use the text editor, that comes with R. If I want to create a new file, I can hit this button. Again it'll give me a new file that I can, you know, save this under a different filename if I want I'm not going to use that now. So I close this window and and that's how you can use the the text editor in R for the Mac. The text editor that comes with R is very simple but it will definitely be sufficient for this class. So there's even though there are other kind of custom text editors that you can, may be able to find on the web and download for free. You don't have to do that, the text editor that comes with R should be sufficient for this class.
