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Data Science Tutorials

How to add labels at the end of each line in ggplot2?, Using the ggplot2 R library, this article shows how to display the last value of each line as a label.

Using either the ggrepel text labeling or the ggplot2 secondary axis functions, many methods are shown.

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R packages required:

tidyverse: data visualization and manipulation made simple

geom_text repel() and geom_label repel() are geoms for ggplot2 that repel overlapping text_labels ()

Let’s load R packages

library(tidyverse)
library(ggrepel)

Set ggplot2 default theme to theme_bw()

theme_set(theme_bw())

Let’s create a some sample data

df <- tibble::tribble(
      ~Species, ~Petal.Length, ~Petal.Width, ~Sepal.Length, ~Sepal.Width,
      "setosa",         1.462,        0.246,         5.006,        3.428,
  "versicolor",          4.26,        1.326,         5.936,         2.77,
   "virginica",         5.552,        2.026,         6.588,        2.974
  )
df
Species    Petal.Length Petal.Width Sepal.Length Sepal.Width
  <chr>             <dbl>       <dbl>        <dbl>       <dbl>
1 setosa             1.46       0.246         5.01        3.43
2 versicolor         4.26       1.33          5.94        2.77
3 virginica          5.55       2.03          6.59        2.97

We can now convert the data into a longer format.

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df_long <- df %>%
  pivot_longer(
    Petal.Length:Sepal.Width,
    names_to = "variable", values_to = "value"
  )
df_long
Species    variable     value
   <chr>      <chr>        <dbl>
 1 setosa     Petal.Length 1.46
 2 setosa     Petal.Width  0.246
 3 setosa     Sepal.Length 5.01 
 4 setosa     Sepal.Width  3.43
 5 versicolor Petal.Length 4.26
 6 versicolor Petal.Width  1.33
 7 versicolor Sepal.Length 5.94
 8 versicolor Sepal.Width  2.77
 9 virginica  Petal.Length 5.55
10 virginica  Petal.Width  2.03
11 virginica  Sepal.Length 6.59
12 virginica  Sepal.Width  2.97

Adding labels to the line ends with ggrepel

Basic line plot examples for the discrete x-axis

plot<- ggplot(df_long, aes(x = Species, y = value, group = variable)) +
  geom_line(aes(color = variable)) +
  geom_point() +
  theme(legend.position = "top")
plot

How to add labels at the end of each line in ggplot2?

Add the last values to the line plot after filtering them.

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It’s the same as the ‘virginica’ species.

data_ends <- df_long %>% filter(Species == "virginica")
plot +
  geom_text_repel(
    aes(label = value), data = data_ends,
    fontface ="plain", color = "black", size = 3
    )

Label variables with their names.

plot2 <- ggplot(df_long, aes(x = Species, y = value, group = variable)) +
  geom_line() +
  geom_point()
plot2 +  geom_text_repel(
    aes(label = variable), data = data_ends,
    color = "black", size = 3
    )

Let’s work on time series data

df2 <- Orange
head(df2)
  Tree  age circumference
1    1  118            30
2    1  484            58
3    1  664            87
4    1 1004           115
5    1 1231           120
6    1 1372           142

As usual, filter the last values

data_ends <- df2 %>%
  group_by(Tree) %>%
  top_n(1, age)
data_ends
Tree    age circumference
  <ord> <dbl>         <dbl>
1 1      1582           145
2 2      1582           203
3 3      1582           140
4 4      1582           214
5 5      1582           177
ggplot(df2, aes(age, circumference)) +
  geom_line(aes(color = Tree)) +
  geom_text_repel(
    aes(label = circumference), data = data_ends,
    size = 3)

Key R functions: Using a supplementary y-axis to show the line labels To produce a second axis on the right, the ggplot2 scale y continuous() method is combined with the option sec.axis.

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The vector of values matching the line ends determines the numbers to be displayed at breaks.

Get the last values vector

data_ends <- df2 %>%
  group_by(Tree) %>%
  top_n(1, age) %>%
  pull(circumference)
data_ends
[1] 145 203 140 214 177

Make a line graph with labels.

ggplot(df2, aes(x = age, y = circumference)) +
      geom_line(aes(color = Tree)) +
      scale_y_continuous(sec.axis = sec_axis(~ ., breaks = data_ends))

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