R Tutorial: How does R Distinguish Variables?

Want to learn more? Take the full course at https://learn.datacamp.com/courses/object-oriented-programming-with-s3-and-r6-in-r at your own pace. More than a video, you'll learn hands-on coding & quickly apply skills to your daily work. --- You’ve already seen the str function for examining the structure of a variable. For example, if you call str on the sleep dataset, you can see that it is a data frame with 20 rows and 3 columns, and you can see some of the details of each column. Now you are going to see some more functions that interrogate your variables to determine their type. The most important of these functions is called class. Going back to the sleep dataset, if you call class on it, then you see the obvious result. That is, the sleep variable has class data-dot-frame, just as you saw when you called the str function. Most of the time class is the only function that you need to use to interrogate the type of your variable. Sometimes, however, you need to dig a little deeper, and there are three more functions to consider. Let’s take a look at a matrix. Notice that the class of this object is "matrix". This is what you might expect, and it’s useful to know, but doesn’t tell you everything. For example, there are different kinds of matrix. As well as numeric matrices, you can also have logical or character matrices. So how do you find out what the matrix contains? In this case, you can use the typeof function. Here you can see that the type is "integer". That is, you have an integer matrix. Now let's look at a numeric matrix. This time, rather than containing integers, you have floating point numbers. Again, of course, the matrix has class "matrix". But now when you call typeof, the return value is "double". This is because typeof returns the type of variable that R understands in its internal C language code. In C, floating point numbers are called doubles, so that's what typeof returns here. The important point is that you can use typeof to p