1.5 Save Your Work In R Objects

Have you ever had an experience where you have forgotten to save your work? It’s a terrible feeling. Saving your work is also important in R. In R, we don’t just do calculations and look at the results on the R console. We usually save the results of the calculations somewhere we can find them later.

Pretty much anything, including the results of any R function, can be saved in an R object. This is accomplished by using an assignment operator, which looks kind of like an arrow (<-). You can make up any name you want for an R object. Most combinations of upper case letters, lower case letters, numbers, or even a period or underscore can be used in the names of R objects, so long as you start the name with a letter.

Here’s a simple example to show how it’s done. Let’s make up a name for an R object; we will call it my_favorite_number. Then let’s think of what our favorite number is (say, 20), and save it in the R object. Go ahead and run the code below to see how this works.

Notice that after you run the code my_favorite_number <- 20 nothing happens. That’s because you saved the number 20 in my_favorite_number, but you didn’t tell R to print it out. Go back and add this line of code to the window above, then run it again:

my_favorite_number

Now it not only saves your favorite number, but prints it out. Notice that you don’t need to use the print() function to print the contents of an R object; you can just type the name of the object.

Now remember, R is case sensitive. Try assigning 5 to num and 10 to NUM.

NOTE: When you save an R object in one of the code windows it will only be saved until you leave the page. If you re-load the page later it won’t be there.

Vectors

We’ve used R objects so far to store a single number. But in statistics we are dealing with variation, which by definition means more than one—and sometimes many—numbers. An R object can also store a whole set of numbers, called a vector. You can think of a vector as a list of numbers (or values).

The R function c() can be used to combine a list of individual values into a vector. You could think of the “c” as standing for “combine.” So in the following code we have created two vectors (we just named them my_vector and my_vector_2) and put a list of values into each vector.

If you ask R to perform an operation on a vector, it will assume that you want to work with the whole vector, not just one of the numbers.

So if you want to multiply each number in my_vector by 100, then you can just write my_vector * 100. Try it in the code window below.

Notice that when you do a calculation with a vector, you’ll get a vector of numbers as the answer, not just a single number.

After you multiply my_vector by 100, what will happen if you print out my_vector? Will you get the original vector (1,2,3,4,5), or one that has the hundreds (100,200,300,400,500)? Try running this code to see what happens.

Remember, R will do the calculations, but if you want something saved, you have to assign it somewhere. Try writing some code to compute my_vector * 100 and then assign the result back into my_vector. If you do this, it will replace the old contents of my_vector with the new contents (i.e., the product of my_vector and 100).

There may be times when you just want to know one of the values in a vector, not all of the values. We can index a position in the vector by using brackets with a number in it like this: [1]. So if we wanted to print out the contents of the first position in my_vector, we could write my_vector[1].

Many functions will take in a vector as the input. For example, try using sum() to total up the five values saved in my_vector. Note that we have already saved some values in my_vector for you.

We will learn about other R objects that help us organize and visualize data as we go along in the class.