Changing color of columns above a certain value in barplot() in R

Question

I am trying to create a barplot that illustrates the number of issue reports for certain issues in an 'imaginary' business. I have used abline() to add a line at a certain value and would like to change the color of the bar above this point. Is such a thing possible to do? Thanks in advance.

My code is as follows:

H<-c(30,35,7,12)
M<-c("Issue 1","Issue 2","Issue 3","Issue 4")
par(mar=c(5,5,5,5))
barplot(H,names.arg=M,ylab="No. of issues",col="light grey",
        main="Issue Analysis",border="black",las=2)
abline(h=20,col="red",lty=2)

And the produced graph is:

BARPLOT

So, you should see that above the red line is the portion of the first two bars that I want to highlight.

Thanks

There is only one value in each var of your "H", I think you shoud have two data set to achive this — Lennon Lee, Aug 16 '22 at 09:11

score 1 · Answer 1 · answered Aug 16 '22 at 09:23

You can divide the bars in two parts (some will be zero) and draw them as stacked bars.

Not to have a line between the stacked bars I first draw the stacked bars without borders and then just the border of the original (non-stacked) bars.

h <- 20
H <- c(30, 35, 7, 12)
M <- paste("Issue", seq_along(H))
H2 <- rbind(pmin(H, h), pmax(H-h, 0))
barplot(H2, names.arg=M, ylab="No. of issues", col=gray(c(.7, .8)),
        main="Issue Analysis", las=2, border=NA)
barplot(H, col=NA, yaxt='n', add=T)
abline(h=h, col="red", lty=2)

score 0 · Answer 2 · answered Aug 16 '22 at 09:40

If you want to use ggplot2, you can use the following function I created (could also use code without function). This is created by slightly modifying the object using ggplot_build. You can define the "threshold" and "colorbar" you want to give the bar area above the threshold. Here you can see an example with threshold 20 and 10:

H<-c(30,35,7,12)
M<-c("Issue 1","Issue 2","Issue 3","Issue 4")
df <- data.frame(H = H,
                 M = M)

library(ggplot2)
library(dplyr)
library(tidyr)
threshold_bar <- function(df, threshold, colorbar){
p <- ggplot(df, aes(x = M, y = H)) +
  geom_bar(stat = "identity") +
  geom_hline(yintercept = threshold, colour = "red")

q <- ggplot_build(p)

q$data[[1]] <- q$data[[1]] %>%
  group_by(group) %>%
  group_modify(~ add_row(.x, .before = 0)) %>%
  fill(everything(), .direction = "up") %>%
  mutate(ymin = ifelse(row_number() == 2 & y > threshold, threshold, ymin)) %>%
  mutate(fill = case_when(ymin == threshold ~ colorbar, 
                          TRUE ~ fill)) %>%
  ungroup()

q <- ggplot_gtable(q)
plot(q)
}

threshold <- 20
colorbar <- "blue"
threshold_bar(df, threshold, colorbar)


threshold <- 10
colorbar <- "blue"
threshold_bar(df, threshold, colorbar)

^{Created on 2022-08-16 by the reprex package (v2.0.1)}

Please note: The function could of course be optimized and extended if you want.

Changing color of columns above a certain value in barplot() in R

2 Answers2