Scale geom_point size to increase size based on distance from zero

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2

You can override the legend guides to make it work. The idea is that you need to specify the number of legend's size.

library(tidyverse) 

set.seed(2018)
year <- rep(c(2015:2018), each = 3)
parameters <- rep(c("length", "weight", "condition"), 4)
z_score <- runif(12, min = -5, max = 5)
df <- tibble(year, parameters, z_score)

# The size of the legends
legend_size <- c(10,8,5,1,5,8,10)

cols <- c("#d73027",
          "darkgrey",
          "#4575b4")

ggplot(df, aes(year, parameters)) +
  geom_point(aes(colour = z_score, size = z_score)) +
  scale_color_continuous(low = "blue", high = "red", breaks = c(-3:3) ) +
  scale_size(breaks = c(-3:3), range = c(1,15)) +
  guides(
    color= guide_legend(), 
    size=guide_legend(override.aes = list(size = legend_size))
  )

Created on 2018-12-19 by the reprex package (v0.2.1)

I wonder why would you want to use 2 aesthetics (size and color) for 1 variable? Is there any extra information added compare to only 1 aesthetic?.

This answer was based on a StackOverflow answer

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