CODEWITHSUNDEEP
rggplot2
FMM
FMM

Reputation: 2005

Manually add a gradient color column in ggplot2

I was looking for a way to dplyr::mutate() a new column based on a color gradient scale. To illustrate, see the following graph:

library(ggplot2)

ggplot(mtcars, aes(mpg, hp, color = hp)) +
  geom_point() +
  scale_color_gradient(low = "red", high = "blue")

Created on 2021-02-08 by the reprex package (v1.0.0)

My goal is to find a function that would map the hp column, and depending on its value, retrieve the hex code. I would like to get all the codes that were used in scale_color_gradient() in a column. For example:

#> # A tibble: 32 x 12
#>      mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb color  
#>    <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <chr>  
#>  1  21       6  160    110  3.9   2.62  16.5     0     1     4     4 #000000
#>  2  21       6  160    110  3.9   2.88  17.0     0     1     4     4 #000000
#>  3  22.8     4  108     93  3.85  2.32  18.6     1     1     4     1 #000000
#>  4  21.4     6  258    110  3.08  3.22  19.4     1     0     3     1 #000000
#>  5  18.7     8  360    175  3.15  3.44  17.0     0     0     3     2 #000000
#>  6  18.1     6  225    105  2.76  3.46  20.2     1     0     3     1 #000000
#>  7  14.3     8  360    245  3.21  3.57  15.8     0     0     3     4 #000000
#>  8  24.4     4  147.    62  3.69  3.19  20       1     0     4     2 #000000
#>  9  22.8     4  141.    95  3.92  3.15  22.9     1     0     4     2 #000000
#> 10  19.2     6  168.   123  3.92  3.44  18.3     1     0     4     4 #000000
#> # … with 22 more rows

Of course, the #000000 is just an example, I would like to retrieve the codes from the colors used in the graph.

Upvotes: 0

Views: 991

Answers (2)

teunbrand
teunbrand

Reputation: 37933

You can use the functions in the scales package to do the same thing as ggplot2 does.

library(ggplot2)
library(scales)
library(dplyr)

df <- mtcars %>% 
  mutate(colour = seq_gradient_pal("red", "blue")(rescale(hp)))

# Showing the colours
ggplot(df, aes(mpg, hp, colour = I(colour))) +
  geom_point()

Proof the colours are the same

g <- ggplot(mtcars, aes(mpg, hp, colour = hp)) +
  geom_point() +
  scale_colour_gradient(low = "red", high = "blue")
g <- layer_data(g)

all(g$colour == df$colour)
#> [1] TRUE

Upvotes: 3

Leonardo
Leonardo

Reputation: 2485

Try this:

p <- ggplot(mtcars, aes(mpg, hp, color = hp)) +
  geom_point() +
  scale_color_gradient(low = "red", high = "blue")

build_p <- ggplot_build(p)
build_p$data[[1]]$colour

Upvotes: 1

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