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summary(cars)
##      speed           dist       
##  Min.   : 4.0   Min.   :  2.00  
##  1st Qu.:12.0   1st Qu.: 26.00  
##  Median :15.0   Median : 36.00  
##  Mean   :15.4   Mean   : 42.98  
##  3rd Qu.:19.0   3rd Qu.: 56.00  
##  Max.   :25.0   Max.   :120.00
library(ggplot2)
ggplot(mtcars,aes(x=factor(1),fill=factor(cyl)))+geom_bar(width=1)+coord_polar("y")+xlab("")+labs(fill='cylinder')

## Cars with 8 cylinders are the most, and with 6 cylinders are the least.
library(ggplot2)
ggplot(mtcars, aes(x=gear))+ geom_bar() + xlab("carb") 

## 3 cars has the most count 15.
library(ggplot2)
ggplot(mtcars, aes(x = factor(gear))) + geom_bar(aes(fill=factor(cyl))) + xlab("Gear") + labs(fill='Cyl')

## gear 3 has the most 8 Cyl. Gear 4 has the most 4 Cyl.
library(ggplot2)
ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + geom_smooth(method='lm',formula=y~x)

## wt and mpg have a negative relationship. Higher wt tends to have lower mpg.
library(ggplot2)
ggplot(mtcars, aes(x=cyl, y=mpg)) + geom_point() + geom_smooth(method='lm',formula=y~x)

## There is lm relationship between cyl and mpg. The purpose is the test a high cyl tends to have a low mpg.