Case Study 1

Background Reading

• Datacamp’s How to Make a Histogram with Basic R
• Datacamp’s How to Make a Histogram with ggplot

Introduction

You are working on a new project and your colleague has asked you to calculate the mean Petal Length in the dataset she collected in the field.

The dataset looks like this:

Sepal.Length	Sepal.Width	Petal.Length	Petal.Width	Species
5.1	3.5	1.4	0.2	setosa
4.9	3.0	1.4	0.2	setosa
4.7	3.2	1.3	0.2	setosa
4.6	3.1	1.5	0.2	setosa
5.0	3.6	1.4	0.2	setosa
5.4	3.9	1.7	0.4	setosa

To work with only one column in the iris dataset, try typing iris$Sepal.Length. What does the $ do?

For the histogram, you can either use the basic hist() function (easier but less powerful) or try to use the geom_hist() function in ggplot (more complicated but much more powerful). See the reading list for hints on these two functions.

When you complete this task, you will have done some ‘reproducible research’ resulting in a script that calculates a statistic and makes a graph. In future lessons we’ll cover how to save the graphic to your hardrive (if you are curious, check out the examples in ?png)

Tasks

• Open the CS01.R file in this assignment
• load the tidyverse package with load(tidyverse)
• In your new script, create a new object called iris by reading in the sample dataset with read_csv("iris.csv")
• Read the help file for the function that calculates the mean (you can run ?mean or use the GUI).
• Calculate the mean of the Petal.Length field and save it as an object named petal_length_mean
• Click ‘source’ in RStudio to run your script from beginning to end
• run test_dir("tests") to see if your script passes all tests for this assignment