Nt1310 Unit 1 Data Visualization

Data Visualization
Dr. Oury September 18, 2014 MA710 - Bentley University

Contents
1 Introduction 1.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 One variable 2.1 1 categorical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 1 numeric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Two variables 3.1 2 categorical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 1 categorical, 1 numeric . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 2 numeric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Three variables 4.1 3 categorical . . . . . . . 4.2 2 categorical, 1 numeric 4.3 1 categorical, 2 numeric 4.4 3 numeric…show more content…
> summary(iris$Petal.Length) Min. 1st Qu. 1.00 1.60 Median 4.35 Mean 3rd Qu. 3.76 5.10 Max. 6.90

This information can be displayed graphically with a box plot. > boxplot(x=iris$Petal.Length)

This is appropriate when the range of values for a numeric variable is normal (bellshaped.)

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3.1

Two variables
2 categorical

In this section we describe two methods to display relative frequency counts for values of two categorical variables. The two variables am and cyl of the mtcars dataframe are presented below to demonstrate both methods. The first method is a partitioned barchart where one variable is used to create the bars, specified by the x parameter, and the other variable is used to partition the bars, specified by the fill parameter. Notice that two different charts can be displayed for a single pair of variables.

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> qplot(data = mtcars, x = amF, fill=cylF)

15 cylF

count

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4cyl 6cyl 8cyl

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0 Automatic Manual

amF

> qplot(data = mtcars, x = cylF, fill=amF)

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count

amF Automatic Manual 5

0 4cyl 6cyl 8cyl…show more content…
The relative frequencies for values of the secondary variable (the variable after the + plus sign) for a single value of the primary variable are displayed using the rectangular regions with the regions determined by the primary variable. The example below presents the cylF and amF variables of the mtcars dataframe. A table of frequency counts of these variables is available from the xtabs function. > xtabs(data=mtcars, formula=~cylF+amF) amF cylF Automatic Manual 4cyl 3 8 6cyl 4 3 8cyl 12 2 Notice the differences between the two mosaic plots below. > mosaic(formula= cylF ~ amF,