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r2 - Math 127B Basic R Lecture 2 Mrinal Raghupathi...

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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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