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')

Answer 2

The solution I came up with is to combine two data.frame and also a variable indicating which groups the observation belongs to. Then, you can use melt function in reshape2 to transform the data into a data.frame ready for plotting. You can use facet_grid or facet_wrap to create separate plots for different variables. This is a way to do it:

library(ggplot2)
library(reshape2)

# Combine two data.frame
df <- rbind(GroupA, GroupB)

# Create variable Group
df$Group <- rep(c("A", "B"), c(dim(GroupA)[1], dim(GroupB)[1]))

# Transform to long format
df <- melt(df, "Group")

ggplot(df, aes(x=Group, y=value)) + geom_boxplot() + facet_grid(~ variable)

Answer 3

Assuming the names of your data sets are grpa (Group A) and grpb (Group B). First add a variable Group to each of them:

grpa$Group <-"A"

grpb$Group <-"B"

Then combine them into a single dataframe

combined <- rbind(grpa,grpb)

Then plot using ggplot like:

ggplot(combined,aes(x= factor(Group), y=V1))+geom_boxplot()

Label as required.

Answer 4

# Adding a variable to the dataframes Group_A & Group_B as done from pervious users
Group_A$fac <- "A"
Group_B$fac <- "B"
Group_c <- rbind(Group_A,Group_B)
df <- melt(Group_c)

#You can plot the same in bwplot from library(lattice) 

bwplot(value~fac|variable,data=df,scales=list(relation="free"),as.table=T)

Answer 5

   par(mfrow=c(1,2))
   summary(A)
   summary(B)
   boxplot(A,ylim=summary(A)[[1]][1]) ##not sure about this just find where y is min
   boxplot(B,ylim=summary(B)[[1]][1]) ## still not sure
    ## adjusts the ylims in a way so that they are easy to compare you can also use boxplot(A,B) but that would make the graph look weird