Library

library(ggplot2)

Question 1

Find the mtcars data in R. This is the dataset that you will use to create your graphics. Show a “summary” of the dataset. Use that data to draw by hand graphics for the next 4 questions.

The Solution

data(mtcars)
summary(mtcars)
##       mpg             cyl             disp             hp       
##  Min.   :10.40   Min.   :4.000   Min.   : 71.1   Min.   : 52.0  
##  1st Qu.:15.43   1st Qu.:4.000   1st Qu.:120.8   1st Qu.: 96.5  
##  Median :19.20   Median :6.000   Median :196.3   Median :123.0  
##  Mean   :20.09   Mean   :6.188   Mean   :230.7   Mean   :146.7  
##  3rd Qu.:22.80   3rd Qu.:8.000   3rd Qu.:326.0   3rd Qu.:180.0  
##  Max.   :33.90   Max.   :8.000   Max.   :472.0   Max.   :335.0  
##       drat             wt             qsec             vs        
##  Min.   :2.760   Min.   :1.513   Min.   :14.50   Min.   :0.0000  
##  1st Qu.:3.080   1st Qu.:2.581   1st Qu.:16.89   1st Qu.:0.0000  
##  Median :3.695   Median :3.325   Median :17.71   Median :0.0000  
##  Mean   :3.597   Mean   :3.217   Mean   :17.85   Mean   :0.4375  
##  3rd Qu.:3.920   3rd Qu.:3.610   3rd Qu.:18.90   3rd Qu.:1.0000  
##  Max.   :4.930   Max.   :5.424   Max.   :22.90   Max.   :1.0000  
##        am              gear            carb      
##  Min.   :0.0000   Min.   :3.000   Min.   :1.000  
##  1st Qu.:0.0000   1st Qu.:3.000   1st Qu.:2.000  
##  Median :0.0000   Median :4.000   Median :2.000  
##  Mean   :0.4062   Mean   :3.688   Mean   :2.812  
##  3rd Qu.:1.0000   3rd Qu.:4.000   3rd Qu.:4.000  
##  Max.   :1.0000   Max.   :5.000   Max.   :8.000

Question 2

Draw a bar graph, that shows the number of each “gear” type in “mtcars”

The Solution in R

ggplot(data=mtcars, aes(x=gear)) + geom_bar(stat="count")

The Solution “by hand”

[The bar graph for ‘gear’ in ‘mtcars’]

Bar Graph

Bar Graph

Question 3

Show a stacked bar graph of the number of each “gear” type and how they are further divided out by “cyl”.

ggplot(mtcars, 
       aes(x = factor(cyl), fill = factor(gear))) +  
       xlab("Values of 'cyl'") +
       ylab("Values of 'count of gear'") +
       geom_bar(color="black")

The Solution “by hand”

[Stack bar graph of the number of each ‘gear’ out by ‘cyl’]

Stacked Bar Graph

Stacked Bar Graph

Question 4

Draw a scatter plot showing the relationship between “wt” and “mpg”.

The Solution in R

ggplot(mtcars, aes(x = wt, y = mpg)) +
       xlab("wt") + ylab("mpg") +
       geom_point() +
       geom_line() +
       ggtitle("Relationship between 'wt' and 'mpg'") +
       stat_smooth(method = "loess", formula = y ~ x, size = 1, col = "red")

The Solution “by hand”

[Scatter plot showing relationship between ‘wt’ and ‘mpg’]

scatter plot

scatter plot

Question 5

Draw a pie chart showing the proportion of cars from the “mtcars” data set that have different “carb” values.

The Solution in R

ggplot(data=mtcars, 
       aes(x = factor(1), fill = factor(carb))) + 
       ylab("Proportions of cars by 'carb' value") + xlab("") +
       geom_bar(width = 1) + 
       coord_polar(theta = "y")

The Solution “by hand”

[Pie chart showing the proportions of cars that have different ‘carb’ values]

pie chart

pie chart