Display a single column value on a ggplot

Question

I'm trying to display summary values on my plot for ease of comparison. Not too sure if I've phrased the question correctly as I haven't found anything other than geom_text references. I'll try to explain my reasoning below.

Base dataframe with two lines, value vs time.

library(tidyverse)

df <- tibble(
  "sample" = as.factor(c(rep("A",6), rep("B",6))),
  "time"   = c(rep(1:6,2)),
  "value1" = c(10,20,30,60,30,30,13,21,32,64,35,32),
  "value2" = c(5,15,20,30,20,10,6,15,22,31,42,11)
)

> df
# A tibble: 12 x 4
   sample  time value1 value2
   <fct>  <int>  <dbl>  <dbl>
 1 A          1     10      5
 2 A          2     20     15
 3 A          3     30     20
 4 A          4     60     30
 5 A          5     30     20
 6 A          6     30     10
 7 B          1     13      6
 8 B          2     21     15
 9 B          3     32     22
10 B          4     64     31
11 B          5     35     42
12 B          6     32     11

Calculate the areas between the two lines and join with the original dataframe. (I've joined the summary data due to assuming it would be easier to display on the plots this way, may be incorrect?)

df <- df %>% 
  group_by(sample) %>% 
  dplyr::summarise(sum1 = sum(value1),
            sum2 = sum(value2),
            auc = abs(sum1-sum2)) %>% 
  dplyr::select(-c(sum1,sum2)) %>% 
  right_join(df)

> df
# A tibble: 12 x 5
   sample   auc  time value1 value2
   <fct>  <dbl> <int>  <dbl>  <dbl>
 1 A         80     1     10      5
 2 A         80     2     20     15
 3 A         80     3     30     20
 4 A         80     4     60     30
 5 A         80     5     30     20
 6 A         80     6     30     10
 7 B         70     1     13      6
 8 B         70     2     21     15
 9 B         70     3     32     22
10 B         70     4     64     31
11 B         70     5     35     42
12 B         70     6     32     11

Plotting the values over time with highlighted area I'm interested in. I have not been able to figure out how to display the auc value on the plot. To clarify, I want to extract the values of 70, 80 and display them, for example, on the bottom right of the faceted graphs. (NOT, for example, displaying a value of 80 on every single point on the plot).

Is this possible? I haven't quite found the best way to go about it yet. Appreciate any help.

df %>% 
      ggplot(aes(x=time,y=value1))+
      geom_line()+
      geom_line(aes(y=value2),color='red')+
      geom_ribbon(aes(ymin = value2, ymax = value1), fill='green', alpha=.3)+
      facet_wrap(~sample)

Answer 1

You can do something like this...

df %>% 
  ggplot(aes(x=time,y=value1))+
  geom_line()+
  geom_line(aes(y=value2),color='red')+
  geom_ribbon(aes(ymin = value2, ymax = value1), fill='green', alpha=.3) +
  geom_text(aes(x = 2, y = 60, label = paste0("AUC = ", auc)), color = "red", data = df %>% distinct(sample, auc)) +
  facet_wrap(~sample)

...which makes this graph:

Answer 2

df %>% 
ggplot(aes(x=time,y=value1))+
 geom_line()+
 geom_line(aes(y=value2),color='red')+
 geom_ribbon(aes(ymin = value2, ymax = value1), fill='green', alpha=.3)+
 facet_wrap(~sample) +
 geom_text(aes(x = 2, y = 60, label = auc))

This gives you what you want I believe. You can relocate the text by changing "2" and "60".