Previously, you learned the basics of data frames. Here, we will review the built-in functions used to filter a data frame. Although a data frame is essentially a list of vectors, we can access it like a matrix since all column vectors are of the same length. To select rows that meet certain conditions, we will supply a logical vector as the first argument of [], while the second is left empty.
In R, these operations can be done with built-in functions. In this section, we will introduce some built-in functions that are most helpful to manipulate data into the form we need as model input or for presentation. Some of the functions or techniques are already presented in the previous chapters.
Most of the code in this section and subsequent sections are based on a group of fictitious data about some products. We will use the readr package to load the data for better handling of column types. If you don't have this package installed, run install...