Package

For this post, we need the ggplot2 and geomtextpath packages.

# Install the packages if not already done
# install.packages("ggplot2")
# install.packages("geomtextpath")

# Load the package
library(ggplot2)
library(geomtextpath)

Default scatter plot in ggplot2

Here’s what the default scatter plot output looks like with ggplot2:

Add trend line with label on top

With the geom_labelsmooth() function, we add a trend line with a label on it!

It has the following arguments:

fill: the background color of the label
method: type of trend wanted. In our case, lm means the ordinary least squared estimator (linear regression). Check the function documentation for available possibilities
size, linewidth and boxlinewidth: define the properties of the text and its box

library(hrbrthemes)
data(iris)

ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) +
  geom_point() +
  geom_labelsmooth(aes(label = 'My Label'), fill = "white",
                method = "lm", formula = y ~ x,
                size = 6, linewidth = 2, boxlinewidth = 0.6) +
  theme_bw() + guides(color = 'none') # remove legend

Multiple groups trend lines with labels

In the case of a multi-group scatter plot, the geom_labelsmooth() function works just as simply:

we add color=Species
we change label = 'My Label' to label = Species

And that’s it!

library(hrbrthemes)
data(iris)

ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +
  geom_point() +
  geom_labelsmooth(aes(label = Species), fill = "white",
                method = "lm", formula = y ~ x,
                size = 3, linewidth = 1, boxlinewidth = 0.4) +
  theme_bw() + guides(color = 'none') # remove legend

Conclusion

In this post, we look at how to use the geomtexpath package to create scatter plots with trend lines and labels. To find out more about how to customize a scatter plot, see the dedicated section.

Scatter plot with trend lines and labels on top

Package

Default scatter plot in ggplot2

Add trend line with label on top

Multiple groups trend lines with labels

Conclusion

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