Adding a simple lm trend line to a ggplot boxplot

Question

When adding a linear model trend line to a boxplot using standard R graphics I use:

boxplot(iris[,2]~iris[,1],col=\"LightBlue\",main=\"Quartile1 (Rare)\")
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Answer 1

The error message is pretty much self-explanatory: Add aes(group=1) to geom_smooth:

ggplot(iris, aes(factor(Sepal.Length), Sepal.Width)) +
  geom_boxplot() +
  geom_smooth(method = "lm", se=FALSE, color="black", aes(group=1))