Translate base R plot to ggplot. Gradient fill rectangles

Question

Could someone help me translate the following base R code to ggplot2:

EDIT - my x values are observations. For example:

x            <-runif(100,min=0,max=60)
lim_x        <-range(x)
lim_y        <-c(0.5,3.5)
probabilities<-cbind(seq(from=0,to=1,length.out=100),
                     c(seq(from=0,to=1,length.out=50),seq(from=1,to=0,length.out=50)),
                     seq(from=1,to=0,length.out=100))

plot(c(lim_x[1],lim_x[2]), c(lim_y[1], lim_y[2]), type = "n",ylab="",xlab="") 


for(i in 1:ncol(probabilities)){
  p <- probabilities[,i]
  gradient.rect(lim_x[1],i-0.5,lim_x[2],i+0.5,nslices=nrow(probabilities),
                reds=1,greens=1-p,blues=1-p)
}

which produces this plot:

Answer 1

This is how I would translate that base R code to ggplot2:

library(ggplot2)

lim_x        <-c(0,60)
lim_y        <-c(0.5,3.5)
probabilities<-cbind(seq(from=0,to=1,length.out=100),
                     c(seq(from=0,to=1,length.out=50),seq(from=1,to=0,length.out=50)),
                     seq(from=1,to=0,length.out=100))


df <- reshape2::melt(probabilities)

ggplot(df, aes(Var1, Var2, fill = value)) +
  geom_tile() +
  scale_fill_gradientn(colours = c("white", "red")) +
  annotate("rect", xmin = min(df$Var1) - 0.5, xmax = max(df$Var1) + 0.5,
           ymin = unique(df$Var2) - 0.5, ymax = unique(df$Var2) + 0.5,
           colour = "black", fill = NA)

^{Created on 2021-09-14 by the reprex package (v2.0.1)}

Alternatively, if you want the exact same colours, you can use:

ggplot(df, aes(Var1, Var2)) +
  geom_tile(aes(fill = I(rgb(1, 1 - value, 1 - value)))) +
  annotate("rect", xmin = min(df$Var1) - 0.5, xmax = max(df$Var1) + 0.5,
           ymin = unique(df$Var2) - 0.5, ymax = unique(df$Var2) + 0.5,
           colour = "black", fill = NA)