Modifying dot charts by grouping variables

In this recipe, we will learn how to make dot charts with grouped variables. Dot charts are often preferred to bar charts because they are less cluttered and convey the same information more clearly with less ink.

Getting ready

We will continue using the citysales.csv example dataset in this recipe. Make sure that you have loaded it into R and type in the recipe at the R prompt. You might also want to save the recipe as a script so that you can easily run it again later. We will need the reshape package to change the structure of the dataset. So, let's make sure we have it installed and loaded:

install.packages("reshape")
library(reshape)

How to do it...

We will first apply the melt() function to the citysales dataset to convert it to long form and then use the dotchart() function:

sales<-melt(citysales)

sales$color[sales[,2]=="ProductA"] <- "red"
sales$color[sales[,2]=="ProductB"] <- "blue"
sales$color[sales[,2]=="ProductC"] <- "violet"

dotchart(sales[,3],labels=sales$City,groups=sales[,2],
col=sales$color,pch=19,
main="Sales Figures",
xlab="Sales Revenue (1,000's of USD)")
How to do it...

How it works...

We first converted the data into long form by applying the melt() function from the reshape library. This is what the new dataset looks like:

City

Variable

Value

Mumbai

ProductA

3

London

ProductB

6

Tokyo

ProductB

7

Seattle

ProductB

11

Seattle

ProductC

12

Tokyo

ProductC

13

Mumbai

ProductC

14

Seattle

ProductA

23

Tokyo

ProductA

24

Berlin

ProductB

34

Berlin

ProductA

36

Berlin

ProductC

44

London

ProductC

56

Mumbai

ProductB

78

London

ProductA

89

Then we add a column called color that holds a different value of color for each product (red, blue, and violet).

Finally, we call the dotchart() function with the values column as the first argument. We set the labels argument to the city names and group the points by the second column (product). The color is set to the color column using the col argument. This results in a dot chart with the data points grouped and colored by products on the y axis.

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