ggplot 이중축 dual axis

Second Axis 추가

https://shanmdphd.rbind.io/post/2018-09-06-dualy/

### DATA -----------------------------------------------------------------------
data <- iris %>% as.data.table()

### EDA ------------------------------------------------------------------------
data[ , .(Sepal.Length, Petal.Width)] %>% summary()

### PLOT -----------------------------------------------------------------------
p1 <- data %>% ggplot(aes(x=1:nrow(data))) +  
  geom_line( aes(y=Sepal.Length, color='SL')) +
  geom_line( aes(y=Petal.Width,  color='PW')) 
p1 <- p1 + labs(x="" , y="Sepal.Length(SL) or Petal.Width(PW)" )
p1

p2 <- data %>% ggplot(aes(x=1:nrow(data))) +  
  geom_line( aes(y=Sepal.Length, color='SL')) +
  geom_line( aes(y=Petal.Width*4,  color='PW')) 
p2 <- p2 + labs(x="", y="Sepal.Length(SL)")
# Adata Second Axis
p2 <- p2 + scale_y_continuous(sec.axis=sec_axis(~./4, name="Petal.Width(PW)"))
p2