R reorder() -reorder columns in ascending order, descending order when setting aes()

Reorder Columns 

<How to make columns in R>
1. make summary (using dplyr)
2. decide x-axis, y-axis
3. draw columns (using ggplot2)

<How to make reordered columns in R> 
During step3, you should use reorder() function in x-axis 

<How to make columns in R>


1. Make Summary 


> library(ggplot2)
> library(dplyr)
> drv_cty<-mpg%>%group_by(drv)%>%summarise(mean_cty=mean(cty))
> drv_cty
   
# A tibble: 3 x 2
drv   mean_cty
<chr>    <dbll>
1 4         14.3
2 f         20.0
3 r         14.1

2. Decide X,Y axis 

 x-axis: drv
 Y-axis: mean_cty



3. Draws columns 

> ggplot(data=drv_cty, aes(x=drv, y=mean_cty))+geom_col()


<How to make reordered columns in R>

STEP 1,2 is same with <How to make columns in R>

3. Draw Reordered Columns 

1. Reorder X-axis in ascending order 

> ggplot(data=drv_cty,aes(x=reorder(drv,mean_cty),y=mean_cty))+geom_col()


2. Reorder X-axis in descending order 

> ggplot(data=drv_cty,aes(x=reorder(drv,-mean_cty),y=mean_cty))+geom_col()