R - Boxplots from different datasets but same color legend

Question

I have two datasets that represent the same, but one from simulated data and other from real data. I want to compare both with boxplots. So far, I did plot them as you can see in the image. The question is, I want each boxplot in a group to have a different color but being the same for both datasets, so it would be only 5 different colors where the simulated data have alpha=0.2. Let say, to compare real 'Dt' 'RFR' with simulated 'Dt' 'RFR' I'd like to have two boxplots with the same color but one "alphaed".

In addition, I don't know how can I show that in a two column legend, one for the real labels and one for the simulated labels (the ones with and 's' at the beggining).

My code for the plot is the following

p <- ggplot()+geom_boxplot(data=simulation,aes(x=param,y=data, fill=algo), alpha=0.2)+
  geom_boxplot(data=ADCF2param_shuffle,aes(x=param, y = data, fill=algo))+
  geom_point(data =gt_vs_fitted,aes(param, y = data), color='red', size=4, shape=18)
p+scale_fill_brewer(palette="YlGnBu") + theme_classic() + labs(y="CCC", x= "Parameters")

Here some sample data. For each 'algo' I have some data of every 'param'. And the same structure in the simulation data.

Answer 1

Try this:

library(tidyverse)

# Made-up data
simulation <- tribble(
  ~param, ~data, ~algo,
  "Dt", 1, "GBR",
  "Dt", 1.3, "GBR",
  "Dt", 1.5, "ETR",
  "Dt", 1.7, "ETR",
  "Dv", 1.5, "ETR",
  "Dv", 1.6, "ETR",
  "Dv", 2, "GBR",
  "Dv", 2.1, "GBR"
)

shuffle <- tribble(
  ~param, ~data, ~algo,
  "Dt", 2.1, "GBR",
  "Dt", 2.2, "GBR",
  "Dt", 2.4, "ETR",
  "Dt", 2.6, "ETR",
  "Dv", 2.4, "ETR",
  "Dv", 2.8, "ETR",
  "Dv", 3.2, "GBR",
  "Dv", 2.9, "GBR"
)

fitted <- tribble(
  ~param, ~data, ~algo,
  "Dt", 1.12, "GBR",
  "Dt", 1.54, "ETR",
  "Dv", 1.56, "ETR",
  "Dv", 2.12, "GBR"
)

joined_df <- bind_rows(
  simulation = simulation,
  shuffle = shuffle,
  .id = "dataset"
)

# Plot
joined_df |> 
  ggplot(aes(param, data, fill = algo)) +
  geom_boxplot(aes(alpha = dataset, linetype = dataset), 
               data = joined_df |> filter(dataset == "simulation")) + 
  geom_boxplot(aes(alpha = dataset, linetype = dataset), 
               data = joined_df |> filter(dataset == "shuffle")) + 
  geom_point(data = fitted, color = "red", size = 2, shape = 18) +
  scale_fill_brewer(palette = "YlGnBu") + 
  scale_alpha_manual(values = c(1, 0.2)) +
  theme_classic() + 
  labs(y = "CCC", x = "Parameters") +
  theme(legend.position = "bottom")

^{Created on 2022-07-04 by the reprex package (v2.0.1)}