How can i annotate with arrows the maximum and the minimum of ggplot in R?-CodePudding

i have a data frame with dates and values :


n = 1000
date = seq(as.Date("2022/1/1"), by = "day", length.out = n)
value = rnorm(n,0,1)
df = tibble(date,value);df

how can i ggplot this data frame and to plot in the geom_line or geom_point two arrows pointing the maximum value and the minimum value of the value variable ?

ggplot(data =df, aes(x = date,y=value))   
  geom_point()


ggplot(data =df, aes(x = date,y=value))   
  geom_line()

Any help ?

CodePudding user response：

It's easiest to create a dataframe of the data for the annotations and then add it to the plot.

Here I make maxmin_df, which contains the details of the maximum and minimum values, and then add a geom_segment() to add them to the ggplot().

You'll need to decide on the look of the line and arrows.

max_df <- tibble(y = max(df$value), 
              yend = y, 
              x = df$date[which(df$value == y)]   lubridate::days(5),
              xend = x   lubridate::days(50))

minmax_df <- bind_rows(max_df,
                       c(tibble(y = min(df$value), 
                                yend = y, 
                                x = df$date[which(df$value == y)]   lubridate::days(5),
                                xend = x   lubridate::days(50))
                         )
                      )


ggplot(data = df, aes(x = date,y=value))   
  geom_point()  
  geom_segment(data = minmax_df, aes(x = xend, xend = x, y = y, yend = yend), colour = "red", arrow = arrow())

CodePudding user response：

Update: One way could be using additional packages like ``ggpmiscorgghighlight`:

ggpmisc

library(ggplot2)
library(ggpmisc)
ggplot(data =df, aes(x = date,y=value))   
  geom_point() 
  geom_point(data = df[which.max(df$value), ], color="red", 
             size=3)  
  stat_peaks(span = NULL,
             geom = "text_s",
             x.label.fmt = "my text",
             segment.colour = "blue",
             arrow = grid::arrow(length = unit(0.1, "inches")),
             position = position_nudge_keep(x = 90, y = 0.1),
             hjust = 0)

gghighlight:

  library(gghighlight)
  library(dplyr)
  library(ggplot2)

  df %>% 
    mutate(my_label = ifelse(value == max(value), "my text", "")) %>% 
    ggplot(aes(x = date,y=value))   
    geom_point() 
    gghighlight(value == max(value), 
                use_direct_label = TRUE,
                label_key = my_label,
                label_params = list(size=3,
                                    color="red"))  
    geom_point(col = "red", size = 3)

by adding unhighlighted_colour = alpha("black", 1), we can keep the color of the original geom_point:

First answer: Maybe this one is also helpful: coloring the max value red:

library(ggplot2)

  ggplot(data =df, aes(x = date,y=value))   
    geom_point() 
    geom_point(data = df[which.max(df$value), ], color="red", 
               size=3)