Conditional text colour based on background colour (High contrast text) for ggplot (geom_col, and geom_text)

Question

Hello you clever R people! I'm trying to create a stack bar plot showing soil thicknesses with a specific background colour and then add labels to the plot that change colour depending on the background colour. I'm very new to R and this is the first time I've attempted something like this. I've worked through several examples and I think I'm getting close but I can't seem to work out how to create a conditional text colour based on the back ground colour. I want something like this example:- https://lara-southard.medium.com/changing-geom-text-color-for-stacked-bar-graphs-in-ggplot-f0e45bfeaa56

My code is messy because it's modified from a worked example Here is my code:-

soil_profile <- cbind.data.frame(
  profile = "",               # Name of the whole profile
  from = c(0,0.41,0.76,1.00,1.45,1.58,1.88),                    # Beginning of each horizon
  to = c(0.41,0.76,1.00,1.45,1.58,1.88,2.48),                    # End of each horizon
  horizon=c('Peaty loam','Loamy peat', 'Humified peat (1)', 'Humified peat (2)', 'Fine sand',
  'Pipe bedding and exclusion zone', 'Pipe'),       # Name of the horizon
  hex = c('#33CCCC', '#008080', '#003366', '#003366', '#F2F2F2', '#A9D18E', '#A9D18E')
)

soil_profile
soil_profile <- soil_profile%>%
 mutate(
    height = to - from 
 )

soil_profile
soil_plot<-ggplot(
 data = soil_profile,
aes(
 x=profile,y=-height,                       # specify x and y axis
fill=fct_reorder(horizon,to,.desc=TRUE)), # make sure that horizons are on the right order
)+
  geom_col(
width=0.8, color= 'white'                                  # Profile width
 )

soil_plot
soil_plot<-soil_plot+
scale_fill_manual(
breaks=soil_profile$horizon,
values=soil_profile$hex)

soil_plot
soil_plot<-soil_plot+
guides(fill=FALSE)+                      # Hide legend
 geom_text(
aes(y=-(from+height/2),label=horizon))
soil_plot
soil_plot+
  scale_x_discrete(position = 'top')+    # Move profile name to the top
labs(
title = "",
y = "Depth (meters)",
x=""
 )+
 theme_minimal() 

Here is the graph I get enter image description here and here is the graph I want enter image description here

I want something like this example:- https://lara-southard.medium.com/changing-geom-text-color-for-stacked-bar-graphs-in-ggplot-f0e45bfeaa56

Answer 1

Create a color palette which assigns to each horizon your desired text color as you did with the fill palette. Afterwards map on the color aes and set your color palette using scale_color_manual:

Note: For an approach to automatically set the text colors see Set a color to show clear the numbers

library(ggplot2)

pal_color <- c(rep("white", 4), rep("black", 3))
names(pal_color) <- soil_profile$horizon

ggplot(
  data = soil_profile,
  aes(
    x = profile, y = -height,
    fill = fct_reorder(horizon, to, .desc = TRUE)
  ),
) +
  geom_col(
    width = 0.8, color = "white"
  ) +
  scale_fill_manual(
    breaks = soil_profile$horizon,
    values = soil_profile$hex
  ) +
  scale_color_manual(
    values = pal_color
  ) +
  guides(fill = "none", color = "none") +
  geom_text(
    aes(
      y = -(from + height / 2), label = horizon,
      color = horizon
    )
  ) +
  scale_x_discrete(position = "top") +
  labs(
    title = NULL, y = "Depth (meters)", x = NULL
  ) +
  theme_minimal()