Homework 3

the following code will make the html font larger

We’ll grade your homework by reading the HTML output

You should write R code anywhere you see an empty R code chunk. You should write English text anywhere you see “…”; please surround it with doubled asterisks (**...**) so that it will show up as boldface and be easy for us to find.

Include reasonable labels (titles, axis labels, legends, etc.) with each of your graphs.

Name: …

Email: …

We’ll use data on housing values in suburbs of Boston. They are in an R package called “MASS.” (An R package is a collection of code, data, and documentation. “MASS” refers to the book “Modern Applied Statistics with S.” R developed from the earlier language, S.) The MASS package comes with the default R installation, so it’s already on your computer. However, it’s not loaded into your R session by default. So we’ll load it via the require() command (there’s nothing for you to do here):

require("MASS")

## Loading required package: MASS

Run ?Boston (outside this R Markdown document) to read the help page for the Boston data frame.

Convert the chas variable to a factor with labels “off” and “on” (referring to the Charles river).

How many rows are in the Boston data frame? How many columns?

What does a row represent? …

What does a column represent? …

Make a density plot (with rug) of tax rates.

Describe the shape of the distribution of tax rates. …

Note that the distribution shape doesn’t make sense in light of the rug representation of the data. Make a histogram of the tax rates.

Why is the second peak of the density plot so large? In what way is the rug representation of the data inadequate? Write a line or two of code to figure it out, and then explain it.

…

Make a barplot of “chas”.

How many neighborhoods are on the Charles river?

Make a single graph consisting of three plots:

• a scatterplot of “nox” on the y-axis vs. “dis” on the x-axis
• a (vertical) boxplot of “nox” left of the scatterplot’s y-axis
• a (horizontal) boxplot of “dis” below the scatterplot’s x-axis

Hint: use layout() with a 4x4 matrix, using the top-right 3x3 corner for the scatterplot, leaving the bottom-left 1x1 corner blank, and using the other parts for the boxplots.

(An optional challenge, worth 0 extra credit points: remove the axis and plot border from each boxplot.)

Look into the highest-crime neighborhood by making a single graph of one column of three rows:

• Find the row number, r, of the neighborhood with the highest “crim”.
• Make a density plot of “crim”. Include a rug to show the data.
• Add a red circle at (x, y) = (max crime rate, 0) to make this maximum crime rate stand out.
• Make a density plot with rug of “medv”, adding a red circle at (x, y) = (medv[r], 0) to see what medv corresponds to the highest crime rate.
• Repeat the last step for “ptratio”.

What do you notice about the ptratio and medv for the highest-crime neighborhood?

…