How to overlay two geom_bar? - r

Question

I'm trying to overlay 2 the bars from geom_bar derived from 2 separate data.frames.
dEQ
lab perc
1 lmP 55.9
2 lmN 21.8
3 Nt 0.6
4 expG 5.6
5 expD 0.0
6 prbN 11.2
7 prbP 5.0
and
LMD
lab perc
1 lmP 16.8
2 lmN 8.9
3 Nt 0.0
4 expG 0.0
5 expD 0.0
6 prbN 0.0
7 prbP 0.0
The first plot is:
p <- ggplot(dEQ, aes(lab, perc)) +
xlab(xlabel) + ylab(ylabel) +
geom_bar(stat="identity", colour="blue", fill="darkblue") +
geom_text(aes(vecX, vecYEQ+1.5, label=vecYlbEQ), data=dEQ, size=8.5) +
theme_bw() +
opts(axis.text.x = theme_text(size = 20, face = "bold", colour = "black")) +
opts(axis.text.y = theme_text(size = 20, face = "bold", colour = "black")) +
coord_flip() +
scale_y_continuous(breaks=c(0,10,20,30,40,50,60),
labels=c("0","","20","","40","","60"),
limits = c(0, 64), expand = c(0,0))
print(p)
but I want to overplot with another geom_bar from data.frame LMD
ggplot(LMD, aes(lab, perc)) +
geom_bar(stat="identity", colour="blue", fill="red", add=T)
and I want to have a legend.

Answer 1

here is an example:
p <- ggplot(NULL, aes(lab, perc)) +
geom_bar(aes(fill = "dEQ"), data = dEQ, alpha = 0.5) +
geom_bar(aes(fill = "LMD"), data = LMD, alpha = 0.5)
p
but I recommend to rbind them and plot it by dodging:
dEQ$name <- "dEQ"
LMD$name <- "LMD"
d <- rbind(dEQ, LMD)
p <- ggplot(d, aes(lab, perc, fill = name)) + geom_bar(position = "dodge")

Answer 2

Though the answer is not directly the requirement of OP, but as this question is linked to many subsequent questions on SO that have been closed by giving the link of this question, I am proposing a method for bar(s) within bar plot construction method in ggplot2.
Example for two bars (group-wise division) within one bigger bar plot.
library(tidyverse)
set.seed(40)
df <- data_frame(name = LETTERS[1:10], provision = rnorm(mean = 100, sd = 20, n = 10),
expenditure = provision - rnorm(mean = 25, sd = 10, n = 10))
df %>% mutate(savings = provision - expenditure) %>%
pivot_longer(cols = c("expenditure", "savings"), names_to = "Exp", values_to = "val") %>%
ggplot() + geom_bar(aes(x= name, y = provision/2), stat = "identity", fill = "blue", width = 0.9, alpha = 0.3) +
geom_col(aes(x=name,y=val, fill = Exp), position ="dodge", width = 0.7) +
scale_y_continuous(name = "Amount in \u20b9")

Answer 3

Another option to overlay your bars without lowering transparency using alpha is to group_by the data based on your fill variable and arrange(desc()) your y variable, using position = position_identity() to overlay your bars and have the highest value bars behind and lower values in front. Then you don't need to change the transparency. Here is a reproducible example:
# Add name for fill aesthetic
dEQ$name <- "dEQ"
LMD$name <- "LMD"
library(dplyr)
library(ggplot2)
dEQ %>%
rbind(LMD) %>%
group_by(name) %>%
arrange(desc(perc)) %>%
ggplot(aes(x = lab, y = perc, fill = name)) +
geom_bar(stat="identity", position = position_identity())
Created on 2022-11-02 with reprex v2.0.2
As you can see the bars overlay while keeping the origin transparency.