library(ggplot2)
suppressWarnings(suppressMessages(library(ggplot2)))

#————————————————————————– # Data set from the package ggplot2

data(package="ggplot2")

auto_data=ggplot2::mpg  #load the data

str(auto_data)
## tibble [234 × 11] (S3: tbl_df/tbl/data.frame)
##  $ manufacturer: chr [1:234] "audi" "audi" "audi" "audi" ...
##  $ model       : chr [1:234] "a4" "a4" "a4" "a4" ...
##  $ displ       : num [1:234] 1.8 1.8 2 2 2.8 2.8 3.1 1.8 1.8 2 ...
##  $ year        : int [1:234] 1999 1999 2008 2008 1999 1999 2008 1999 1999 2008 ...
##  $ cyl         : int [1:234] 4 4 4 4 6 6 6 4 4 4 ...
##  $ trans       : chr [1:234] "auto(l5)" "manual(m5)" "manual(m6)" "auto(av)" ...
##  $ drv         : chr [1:234] "f" "f" "f" "f" ...
##  $ cty         : int [1:234] 18 21 20 21 16 18 18 18 16 20 ...
##  $ hwy         : int [1:234] 29 29 31 30 26 26 27 26 25 28 ...
##  $ fl          : chr [1:234] "p" "p" "p" "p" ...
##  $ class       : chr [1:234] "compact" "compact" "compact" "compact" ...
#convert int to char 

auto_data$year_C=as.factor(auto_data$year)
auto_data$cyl_C=as.factor(auto_data$cyl)

#--------------------------------------------------------------------------
# Initial ggplot
#Plot a single metric / numeric variable, 
#for example, "cty"
#We require an index set to create the plot
#So we consider number of rows - use nrow(auto_data)

n=nrow(auto_data)

rowind = seq(1,n) #alternate to 1:n is the function seq()


#Layer 2 Choosing a geometry to plot 
# here we use points 

ggplot(auto_data, aes(x=rowind,y=cty)) + 
  geom_point() 

#Layer 3 aesthetics to plot 
#Three options: size, shape, color

ggplot(auto_data, aes(x=rowind,y=cty)) + 
  geom_point(size=5)