Plot background colour in gradient

Question

This code produces the first plot below:

water.height <- seq(0, 5, 1)
y <- seq(0, 1500, length.out = 6)
df <- data.frame(water.height, y)

library(g         


        

Answer 1

I used Kamil Slowikowski's example to build a simpler function that generates linear gradients depending on a series of values. This can be of use if you have a relationship of some kind between three variables (eg. y~x*z where z also varies over x). Then you just plot y~x and have z~x as a color gradient in the background.

water.height <- seq(0, 5, 1)
y <- seq(0, 1500, length.out = 6)
z <- rnorm(6, 10, 1)
df <- data.frame(water.height, y, z)

grad_by_val <- function(x, y, cols = blues9) {
  require(grid)
  y <- y[order(x)]
  ys <- (y - min(y)) / diff(range(y))
  cols <- colorRamp(cols)(ys) / 256
  colnames(cols) <- c("red", "green", "blue")
  cols <- apply(cols, 1, function(z) do.call(rgb, as.list(z)))
  mat <- matrix(cols, ncol = length(x))
  rasterGrob(
    image = mat,
    width = unit(1, "npc"),
    height = unit(1, "npc"),
    interpolate = TRUE
  )
}

library(ggplot2)
ggplot(df, aes(water.height, y)) + geom_blank() + theme_bw() +
  annotation_custom(
    grob = grad_by_val(df$water.height, df$z),
    xmin = -Inf,
    xmax = Inf,
    ymin = -Inf,
    ymax = Inf
  ) +
  geom_point(
    size = 5,
    color = "#FFFFFF",
    fill = "#000000",
    shape = 21
  )

To add a legend see here.