A list is a great tool to store many kinds of object in the order expected. We can include matrices, vectors data frames or lists. We can imagine a list as a bag in which we want to put many different items. When we need to use an item, we open the bag and use it. A list is similar; we can store a collection of objects and use them when we need them.
We can use list() function to create a list.
Select Elements from List
After we built our list, we can access it quite easily. We need to use the [[index]] to select an element in a list. The value inside the double square bracket represents the position of the item in a list we want to extract. For instance, we pass 2 inside the parenthesis, R returns the second element listed.
Let's try to select the second items of the list named my_list, we use my_list[[2]]
Built-in Data Frame
Before to create our own data frame, we can have a look at the R data set available online. The prison dataset is a 714x5 dimension. We can get a quick look at the bottom of the data frame with tail() function. By analogy, head() displays the top of the data frame. You can specify the number of rows shown with head (df, 5). We will learn more about the function read.csv() in future tutorial.
