R: Convert data.frame to color matrix using ggplot2?

Question

Does anyone know how to use ggplot2 to convert a data frame in R with continous values into a pretty figure. This would be similar to the answer from this post but with ggplot2.

Is this possible?

New to R and ggplot2 so thanks in advance for any advice.

Answer 1

Here's an example using the mtcars data (scaled to give comparable values, so the numbers don't mean much).

The key things are the use of gather to tidy the data, geom_tile filled by value, and geom_text for the labels. Everything else is just manipulation of that particular data frame.

You could also just use one of the scale_fill_gradient geoms.

library(tidyverse)
library(viridis)

mtcars %>% 
  scale() %>% 
  as.data.frame() %>% 
  rownames_to_column(var = "make") %>% 
  gather(var, val, -make) %>% 
  ggplot(aes(var, make)) + 
    geom_tile(aes(fill = val)) + 
    geom_text(aes(label = round(val, 2)), 
              size = 3) + 
    coord_fixed() + 
    scale_fill_viridis() + 
    guides(fill = FALSE)

Or using:

+ scale_fill_gradient2(midpoint = 1.5)