Two boxplots on the same graph

Question

I have two different datasets with different numbers of observations. I would like to plot two boxplots on the same graph so it's easier to make comparison. I could plot one boxplot, but that would be hard to spot any discrepancy without them side by side.

I have some fake data.

Group A
V1    V2   V3    V4     V5
6.5   2    11    0.5    6
7     1    8     0.34   8
5.4   4    7.8   0.45   5
3.4   6    9.1   0.72   5

Group B
V1    V2   V3    V4     V5
5.0   5    9     0.4    7
2     7    5.2   0.69   5
3.2   2    2.9   0.79   2
6.8   9    6.5   0.43   6
4.7   3    3.8   0.49   4
5.5   4    7.4   0.94   3

I don't know how to graph this, so I don't have an example. I'll try my best to describe the plot. I would like to plot Variable 1 for Group A and B on the same graph. So on one graph, I would have a boxplot for Group A and another boxplot for Group B filled with data from V1. So the two boxplots would be side by side. With 5 variables, I would have 5 graphs, each with 2 boxplots side by side. Please let me know if I'm not being clear. Thank you.

Answer 1

ggplot works best with "long format" data (e.g., with a column for each of value, variable, and group). You can rearrange your data as follows:

A <- read.table(text='V1    V2   V3    V4     V5
6.5   2    11    0.5    6
7     1    8     0.34   8
5.4   4    7.8   0.45   5
3.4   6    9.1   0.72   5', header=TRUE)

B <- read.table(text='V1    V2   V3    V4     V5
5.0   5    9     0.4    7
2     7    5.2   0.69   5
3.2   2    2.9   0.79   2
6.8   9    6.5   0.43   6
4.7   3    3.8   0.49   4
5.5   4    7.4   0.94   3', header=TRUE)

d <- rbind(cbind(stack(A), group='A'), cbind(stack(B), group='B'))

The first few rows look like this:

head(d)

##   values ind group
## 1    6.5  V1     A
## 2    7.0  V1     A
## 3    5.4  V1     A
## 4    3.4  V1     A
## 5    2.0  V2     A
## 6    1.0  V2     A

Now we can plot like so:

library(ggplot2)
ggplot(d, aes(group, values)) + 
  geom_boxplot() +
  facet_wrap(~ind, scales='free_y')