How to draw upper & lower bound within a Scatter plot?-CodePudding

I have a scatter plot and I have to show boundaries of y values on it. geom_smooth indicates mean or median values, but I have to indicate maximum and minimum values. How to plot the green lines?

Code:

library(ggplot2)
suaon <- mtcars
pla <- ggplot(data = suaon, mapping = aes(x = mpg, y = wt))
pla <- pla   geom_point(mapping = aes(color = cyl), size = 1.4)
pla <- pla   geom_smooth(span = 0.4, method = "loess", se = FALSE,color = "red", size = 0.8, alpha = 0.1)
pla <- pla   labs(x = "MPG", y = "WT")
pla

CodePudding user response：

If your looking for a simple solution then you can use two for loops. One for the maximum values and one for the minimum values.

I haven't tidied up the code and I'm sure there are better ways but this works.


library(tidyverse)
library(ggplot2)
suaon <- mtcars

##arrange by wt so that the largest wt values are first in the data frame.
max_dat <- suaon %>% arrange(-wt) %>% mutate(max_val = F)

##loop through dataframe checking if the mpg value for i is greater than the current mpg value
##if it is, then include this point as a maximum value and update current_x to the mpg value for row i.

current_x = 0
for(i in 1:nrow(max_dat)){
  if(max_dat$mpg[i] > current_x){
    max_dat$max_val[i] <- T
    current_x <- max_dat$mpg[i]
  }
}
max_dat <- max_dat %>% filter(max_val == T)


min_dat <- suaon %>% arrange(mpg) %>%  mutate(min_val = F)
current_min = max(min_dat$wt)
i <- 1
for(i in 1:nrow(dat)){
  if(min_dat$wt[i] < current_min){
    min_dat$min_val[i] <- T
    current_min <- min_dat$wt[i]
  }
}
min_dat <- min_dat %>% filter(min_val == T)


pla <- ggplot(data = suaon, mapping = aes(x = mpg, y = wt))
pla <- pla   geom_point(mapping = aes(color = cyl), size = 1.4)
pla <- pla   geom_smooth(span = 0.4, method = "loess", se = FALSE,color = "red", size = 0.8, alpha = 0.1)
pla <- pla   labs(x = "MPG", y = "WT")
pla <- pla   geom_line(data = max_dat, aes(x = mpg, y = wt))   
pla <- pla   geom_line(data = min_dat, aes(x = mpg, y = wt))