R ggplot geom_point color gradient based on variable

Question

I am trying to plot London postcodes with ggplot, and I would like the value of colour of each point to vary based on a 3rd variable. The code I have for the initial plot is:

gg <- ggplot() + geom_point(data=joined_data, aes(x=V3, y=V4), color = '#800080', size=0.2, alpha=0.5)
print(gg)

this is all set to a single colour though, how can I set the colour value to vary based on the 3rd variable?

Answer 1

Assuming V5 is your 3rd variable (It must be a column in joined_data.

ggplot(joined_data, aes(x = V3, y = V4, color = V5)) + geom_point()

Answer 2

You must set the colour aesthetic first, then use a continuous color scale to choose the gradient of colors.

I have used the built-in data set iris , transformed.

library(ggplot2)

ggplot(df1, aes(Sepal.Length, Sepal.Width, colour = clr)) +
  geom_point(size = 1, alpha=0.5) +
  scale_color_gradient(low = "#800080", high = "#FF00FF")

Data.

The ave instruction creates a color column clr , depending on the maxima of Sepal.Length by Species .

df1 <- iris
df1$clr <- ave(df1$Sepal.Length, df1$Species, FUN = function(x){
  runif(length(x), 0, max(x))
})