R Tutorial: ggplot2 layers

Key Takeaways

now that we have some idea about the different grammatical elements of graphics let's see how this works in practice the grammar of graphics is implemented in art using the ggplot2 package there are two key functions that ggplot2 serves first we construct plots by layering grammatical elements on top of each other second we use aesthetic mappings to bridge the link between data and its visual interpretation we are going to go through each grammatical element in depth in this and the next course here I'll introduce the data set which will be used throughout the videos and we'll go over some simple examples the bottom layer is the data element obviously we need some data to plot I'm going to use several different data sets in the course videos one which is a classic iris dataset collected by Edgar Anderson in the 1930s and thereafter popularized by Ronald Fisher the data set contains information on three iris species setosa versicolor and virginica four measurements were taken from each plant the petal length and width and the staple length and width you're probably familiar with petals there at the colorful part of a flower sepals are the outer leaves of the flower they are typically green but in this case they're all so colorful there are 50 specimens in each species the data is stored in an object called iris there are five variables the species and one for each of the properties which were measured the next layer will add is the aesthetics element which tells us which scales we should map our data on to this is where the second main component of the grammar of graphics comes into play on top of layering the grammatical elements it's here that we establish our aesthetic mappings in this case we are going to make a scatter plot so we're going to map sepal dot lengths onto the X aesthetic and sepal dot widths onto the Y aesthetic the next element is the geometry element this allows us to choose how the plot will look after we've established our three essential layers we have enough instructions to make a basic scatter plot it's pretty rough so to get it more meaningful and cleaner visualization we'll have to use the other layers the next layer we'll look at is the themes element it controls all the non data ink on our plot which allows us to get a nice looking meaningful and publication quality plot directly in our we'll discuss the remaining grammatical elements in the next course for now let's begin by exploring these Const