Adding regression line in ggplot2

Question

I'm trying to add a regression line to my scatterplot using the following snippet of code


library(ggplot2)
CouncilNames <- c("Antrim and Newtownabbey", "Armagh City, Banbridge and Craigavon", "Causeway Coast and Glens", "Lisburn and Castlereagh", "Mid and East Antrim", "Mid Ulster", "Newry, Mourne and Down")
NumberOfFoodPlaces <- c(110, 170,124, 94, 114, 140, 129)
NumberOfStrayDogs <- c(525, 878, 454, 409, 762, 455, 894)

df <- data.frame(CouncilNames, NumberOfStrayDogs, NumberOfFoodPlaces)
df


plot <- ggplot(df, aes(x=NumberOfFoodPlaces, y=NumberOfStrayDogs, group = CouncilNames, 
                       colour = CouncilNames)) + 
  geom_point() + labs(y="No. of Stray Dogs", x = "No.of Food Establishments") + 
  ggtitle("Correlation between the No. of Stray Dogs and the No.of Food Establishments")
plot

plot + geom_smooth(formula = y ~ x, method = "lm")

cor(df$NumberOfFoodPlaces, df$NumberOfStrayDogs)
test <- cor.test(df$NumberOfFoodPlaces, df$NumberOfStrayDogs)
test

However, the regression line isn't appearing and the only issue I can see is > plot `geom_smooth()` using formula 'y ~ x' is highlighted red in the console. Anyone any ideas?

Welcome to stack ! Please, try to give a minimal reproducible example by giving a toy dataset or using dput on your data, see minimal reproducible example — denis
– denis, Commented Apr 11, 2021 at 22:38
Hi @denis! Please see above the amended code of the exact plot I am creating — userhelp
– userhelp, Commented Apr 11, 2021 at 22:51

Ian Campbell · Accepted Answer · 2021-04-11 22:56:07Z

5

The geom_smooth function operates by color and group. Since each color has only a single point, a line cannot be created. Instead, you must move these aesthetics to geom_point so that all of the data is considered by geom_smooth.

ggplot(df, aes(x=NumberOfFoodPlaces, y=NumberOfStrayDogs)) + 
  geom_point(aes(colour = CouncilNames, group = CouncilNames)) +
  labs(y="No. of Stray Dogs", x = "No.of Food Establishments") + 
  ggtitle("Correlation between the No. of Stray Dogs and the No.of Food Establishments") +
  geom_smooth(formula = y ~ x, method = "lm")

answered Apr 11, 2021 at 22:56

Ian Campbell

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1 Comment

userhelp Over a year ago

Ah that make's total sense now!! Thank you so much

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