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 co, the function getwd. And you'll see that I've loaded up R here and it's, and it sets my working directory to /users/areyoupaying, which, on the mac is just your home directory. So this may work, but if you store all your files in your home directory. But you may want to change into your working directory to be something else if you happen to store all your data and code files in a different directory may be a sub-directory. So for example, I can go to the misc menu here and 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. So if this file is in my working directory, then I'll be able to read the data and it'll load 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 can 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 in this directory. So I'm going to, now I can read the file into R by typing, using read.csv. And now you can see that that data will appear in R. So, so knowing what your working directory is and being able to set it is important because then it will give you, it will give you access to all of the files that you need in R. In particular, when you save files say from the web onto 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 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 uh,I'm in R, I can say change direct, 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 get WD, you'll see that it as set the working directory to be my Coursera folder. So now if you save files in there they will be there then you can, and you can read them from R. So that may be the the easiest thing for one to do. So one thing that you are going to have to do a lot of in this course is write code in R and to and you are 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 est, 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 my function which I'll call myfunction. and, I can, it, it will start indenting things. So I can say, you know, x is R norm, hundred. This function, is just going to just take the mean of x here. So, actually let me just change this to y. And, and it just returns to mean, and so it ignores the argument for now. So and then, and then one thing you are going to do is, kind of, figure out how to get this code into R. So what you'll notice, if I just type myfunction 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 workspace. 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 code is to hit Select All, so that's Command-A, or you can go to the Edit menu and just hit Select All. And then Command c copies the code and then I can click into my console window over her I hit a, a Command v and, and then return and it will paste myfunction into R. So now, if I typed ls, you will see that myfunction is an object in my workspace. I can say myfunction, and it will return the mean of 100 random global 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 going to save it as myfunction, it's typical to add the .r expression for code file and I can hit save. And so now, I can double check my working directory make sure I'm in the right place here. Yeah, I'm in my Coursera working directory. Uh,if I type dir you'll see that the myfunciton.r file is there now. So I'm just source the file myfunction.r. And it'll have the same, it'll 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 we'll call it second to indicate it's a second function. And it's going to take the input x, whoop, excuse me. Wm, and it's going to add a little bit of noise to it [SOUND] and that's all it's going to do to return that. So so, would now, before I do anything I need to, now that I have changed the file I need to save it. So I'll just go to File and then Save or you can do Command s and now I can source my this this file into R again. And you'll notice that when 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'd say second, I'd say 4 and then return 4 plus a little bit of noise. If I do it again, it will be 4 plus a little bit of more noise. I can give it a, you know, 4 through 10 and it gives me each one of those numbers with 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 wanted to create a new file I could hit this button. again, it will give me a new file and I can save this under a different file name, if I want. I'm not going to use that now, so I can close this window. And that's how we can use the text editor in R for Mac. The text editor that comes with R is very simple, but it'll definitely be sufficient for this class. Even though there are other kind of custom text editors that you can maybe able to find on the web download for free, you don't have to do that. The text editor that comes with R should be sufficient for this class.
