Grouping bar plots

Question

I'm trying to group two barcharts, but I haven't been successful so far... I followed this example, but the output is not as desired. The bars are one behind the other instead of next to each other.

Here's the line of code I use:

  barplot(as.matrix(counts),xaxt='n', col=c("white","blue"), ylim=c(0.1,1300), axes=FALSE,  beside=T, space = 1.4, mar=c(5,5,5,5))

When I try this...

> barplot(as.matrix(counts), beside = TRUE)
> barplot(as.matrix(counts), beside = TRUE, space = c(0, 1.4))

... I get this plot:

And this is my data frame, in case that causes the problem:

> counts
     V1  V2
1    26  50
2    50  86
3    86  50
4    50  50
5    50  50
6    50 100
7   100 150
8   150 350
9   350  50
10   50  28
11   28 300
12  300 250
13  250 300
14  300 250
15  250 300
16  300 500
17  500 400
18  400   0
19  600   0
20  500   0
21 1250   0

> dput(counts)
structure(list(V1 = c(26, 50, 86, 50, 50, 50, 100, 150, 350, 
50, 28, 300, 250, 300, 250, 300, 500, 400, 600, 500, 1250), V2 = c(50, 
86, 50, 50, 50, 100, 150, 350, 50, 28, 300, 250, 300, 250, 300, 
500, 400, 0, 0, 0, 0)), .Names = c("V1", "V2"), row.names = c(NA, 
-21L), class = "data.frame")

Any ideas?

Answer 1

I think the problem is that you only provide one space value. From ?barplot: " If height is a matrix and beside is TRUE, space may be specified by two numbers, where the first is the space between bars in the same group, and the second the space between the groups. If not given explicitly, it defaults to c(0,1) if height is a matrix and beside is TRUE".

Try this:

barplot(as.matrix(counts), beside = TRUE)
barplot(as.matrix(counts), beside = TRUE, space = c(0, 1.4))

Update following comments
Given that you seem to want bars grouped by row, rather than column (referring to the original data), you need to transpose your matrix to a 'wide' format. In barplot each column of the input matrix corresponds to a group of bars, and each row to different bars within groups. As your original data was organized, the two columns V1 and V2 represented the groups. Thus the plot resulting from my script above have two groups with 21 bars each. After transposing, you will get a plot with 21 groups with two bars each.

barplot(t(as.matrix(counts)), beside = TRUE)

I add a ggplot example for comparison. In ggplot the data should be a data frame in a long format. Thus, first we need to 'melt' the data. Here I use the melt function from package reshape2. You find several nice ggplot examples here.

library(reshape2)
library(ggplot2)

df <- melt(counts)
ggplot(data = df, aes(x = as.factor(Var1), y = value, fill = Var2)) +
  geom_bar(stat = "identity", position = "dodge")