反转默认比例渐变ggplot2

Question

I am newbie, I am trying to desing a heat map. This is my code:

ggplot(gd, aes(Qcountry, Q6_1_Q6d), order = TRUE) +
  geom_tile(aes(fill = prob), colour = "white") +
  theme_minimal() +
  labs( y = "Main reason for mobility", x = "Country") +
  theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.3)) +
  scale_fill_gradient(name = "(%)")

Which produces a perfect chart, my problem is low levels are dark blue, and higher values are light blue, which is not intuitive. Most common way to do is use rev() . But in my case I dont know how to. So, is it possible to reverse this default scale ? This is the legend

Other question, is there a way to create a scale gradient only with one colour. I mean, scale_fill_gradient/scale_fill_gradientn need to set a low color and high color (low = "", high = "") and I want to change the blue by red.

Thanks so much for your support.

Answer 1

?scale_colour_gradient shows the default values of low = "#132B43" and high = "#56B1F7" .

Simply switch those around:

ggplot(faithfuld, aes(waiting, eruptions)) +
    geom_raster(aes(fill = density)) +
    scale_fill_continuous(high = "#132B43", low = "#56B1F7")

Personally, I think this is less intuitive than the default.

---

Alternatively, you can use a reverse scale, but this will also flip the legend to start at the top:

ggplot(faithfuld, aes(waiting, eruptions)) +
    geom_raster(aes(fill = density)) +
    scale_fill_continuous(trans = 'reverse')

Answer 2

you can use the color palettes from RColorBrewer (link) library and assign the direction of the color gradient

library(RColorBrewer)
library(ggplot2)

ggplot(df, aes(x, y)) +
  geom_tile(aes(fill = z, width = w), colour = "grey50") +
  scale_fill_distiller(palette ="RdBu", direction = -1) # or direction=1


# data
  df <- data.frame( x = rep(c(2, 5, 7, 9, 12), 2),
                    y = rep(c(1, 2), each = 5),
                    z = rep(1:5, each = 2),
                    w = rep(diff(c(0, 4, 6, 8, 10, 14)), 2))