Math 127B, Basic R, Lecture 2
Mrinal Raghupathi
Wednesday, April 6, 2011
Administrivia
Today we will learn about R’s basic plotting features, basic list operations, and how to create our
own commands.
Reminders
1. Homework 9 is due Thursday, 4/7 in recitation.
2. Quiz in recitation over chapter 28 on 4/27.
1
Basic plots
Let’s begin by creating some data to work with. We will create two sets of data. You can copy and
paste the data from the file on the website called cigarette.txt.
The first list is the tar content in mg for 25 brands of cigarette. The second list is the nicotine
content for the same 25 brands. Let’s create two lists and give them the names
tar
and
nic
.
What is the average and sd of the two lists?
1.1
Are tar and nicotine content related?
A good way to answer a question like this, is to use a scatter plot. The command
plot
allows us
to plot two lists. Type
plot(tar, nic)
.
Does the resulting plot indicate a relationship between the two variables?
One way to check the strength of a relationship is to use the find the SD line and the coefficient of
correlation
r
. The command cor computes the coefficient of correlation between the two variables.
Type
cor(tar, nic)
.
What is the value of the coefficient of correlation? What happens if you type
cor(nic, tar)
.
1
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1.2
Histograms
We can use R to produce a histogram.
The command is called
hist
.
Typing
hist(tar)
will
produce a histogram of the tar variable.
You can increase the number of bins by typing using the
breaks
option. So
hist(tar, breaks
= 12)
will produce a plot with more intervals.
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 Spring '11
 Staff
 Math, Statistics, ASCII, Tar

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