Add legend to “geom_bar” using the ggplot2 package

Question

I am a newbie to R, so please pardon my ignorance. I made a pseudo-stacked barplot in which I drew 4 sets of bars on top of each other using geom_bar. There are 4 health sta

Answer 1

I see that @Brandon Bertelsen has posted a great answer. I would like to add some code that addresses additional details mentioned in the original post:

1. After you reshape your data and map health status to fill, ggplot will create the legend automatically.
2. I suggest using scale_fill_manual() to get the exact grays mentioned in the original post.
3. theme_bw() is a handy function to quickly get a black and white look to your plot.
4. The plotting order of factor levels/colors can be controlled by specifying the desired order with the levels argument of factor().
5. A dodged barplot (instead of stacked) may have some advantages for this data set.

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library(reshape2)
library(ggplot2)

x <- as.data.frame(list(variable=c("QUAG", "QUKE", "QUCH"), 
                        alive=c(627, 208, 109),  infected=c(102, 27, 0), 
                        dead=c(133, 112, 12), sod.dead=c(49, 8, 0)))

# Put data into 'long form' with melt from the reshape2 package.
dat = melt(x, id.var="variable", variable.name="status")

head(dat)
#    variable   status value
# 1      QUAG    alive   627
# 2      QUKE    alive   208
# 3      QUCH    alive   109
# 4      QUAG infected   102
# 5      QUKE infected    27
# 6      QUCH infected     0

# By manually specifying the levels in the factor, you can control
# the stacking order of the associated fill colors.
dat$status = factor(as.character(dat$status), 
                    levels=c("sod.dead", "dead", "infected", "alive"))

# Create a named character vector that relates factor levels to colors.
grays = c(alive="gray85", dead="gray65", infected="gray38", sod.dead="black")

plot_1 = ggplot(dat, aes(x=variable, y=value, fill=status)) +
         theme_bw() +
         geom_bar(position="stack") +
         scale_fill_manual(values=grays)

ggsave(plot=plot_1, filename="plot_1.png", height=5, width=5)

# You may also want to try a dodged barplot.
plot_2 = ggplot(dat, aes(x=variable, y=value, fill=status)) +
         theme_bw() +
         geom_bar(position="dodge") +
         scale_fill_manual(values=grays)

ggsave(plot=plot_2, filename="plot_2.png", height=4, width=5)

Answer 2

You need to reshape your data.

library(reshape)
library(ggplot2)

x <- as.data.frame(list(variable=c("QUAG", "QUKE", "QUCH"), alive = c(627,208,109),  infected = c(102,27,0), dead = c(133,112,12), sod.dead=c(49,8,0)))

x <- melt(x)
colnames(x) <- c("Type","Status","value")

ggplot(x, aes(Type, value, fill=Status)) + geom_bar(position="stack")