Gradient colour fill a barplot in ggplot2-CodePudding

I'd like to gradient fill a ggplot2 bar plot based on the values of Y, but I'd like to manually set the colours.

I'd like the red to appear when the Y value is equal to 2, rather than the maximum value of Y in the data frame.

CodePudding user response：

If you know a priori what the values are that you'd like to be red (in your case, 2), you can just set the midpoint at half of that (1).

Your example, but with an extra data point to illustrate:

# d <- data.frame(x = 1:4, y= c(0.1, 0.3, 1, 0.6))
d <- data.frame(x = 1:5, y= c(0.1, 0.3, 1, 0.6, 2.0))
vals <- lapply(d$y, function(y) seq(0, y, by = 0.01))
y <- unlist(vals)
mid <- rep(d$x, lengths(vals))
d2 <- data.frame(x = mid - 0.4, xend = mid   0.4, y = y, yend = y)

ggplot(data = d2, aes(x = x, xend = xend, y = y, yend = yend, color = y))  
  geom_segment(size = 2)  
  scale_color_gradient2(low = "green4", 
                        mid = "yellow", 
                        high = "red", 
                        midpoint = 1)   # changed here
  coord_cartesian(ylim = c(0 , 2))

As noted in the comments on the other answer, you won't see red in your original data - rerun the code here with your original dataset to see the result.

CodePudding user response：

Does this work? Just switched to scale_color_gradientn which allows us to use the values = call where we specify three values for the respective colours. (And a couple of other small changes.)

    
    ggplot(data = d2, aes(x = x, xend = xend, y = y, yend = yend, color = y))  
      geom_segment(size = 2)  
      scale_y_continuous(limits = c(0, 2))  
      scale_color_gradientn(colours = c("green4", "yellow", "red"), 
                            values = c("0", max(d2$y)/2, "2"))