Grouping bars in a ggplot2 [duplicate]

Question

Possible Duplicate:
Order Bars in ggplot2 bar graph

I have a dataset and I would like to have a ggplot bar-plot depicting the proportions for one of the variables and sort or order the bars based on another variable. Here is an example of the dataset.

grouping,category,domain
6,W,ced0.11
1,none,ced1.1
2,none,ced1.1
3,Z,ced1.5
2,Z,ced1.7
3,Z,ced1.3
3,none,ced1.6
2,none,ced1.1
1,Z,ced1.1
4,none,ced0.8
4,W,ced0.6
4,W,ced0.6
2,Z,ced1.5
2,W,ced1.6
4,Y,ced0.16
3,Z,ced1.5
4,Y,ced0.15
4,W,ced0.15
4,Y,ced0.24
6,W,ced0.8
4,Y,ced0.4
4,none,ced0.19
4,W,ced0.5
4,W,ced0.10
4,W,ced0.9
4,W,ced0.3
1,Z,ced1.6
4,W,ced0.9
4,W,ced0.15
1,Z,ced1.1
4,Y,ced0.19
6,W,ced0.4
4,W,ced0.16
4,W,ced0.6
4,W,ced0.5
2,Z,ced1.7
4,W,ced0.9
4,Y,ced0.1
4,W,ced0.2
4,Y,ced0.21
2,W,ced0.3
4,Y,ced0.21
4,W,ced0.10
1,Z,ced1.2
4,Y,ced0.16
1,Z,ced1.2
1,Z,ced1.2
5,W,ced0.23
4,Y,ced0.1

and the code below for importing and display a bar chart.

library(ggplot2)
ex1.dta <- read.csv("../../Datasets/ex1.txt",sep=",",header=TRUE)

#sort the data frame
ex1.dta2 <- transform(ex1.dta,domain=reorder(domain,category))

ggplot(ex1.dta2,aes(domain,fill=category)) +
  geom_bar(position="fill") + 
  scale_y_continuous(name="Proportion") + 
  scale_x_discrete(name="domains") +
  scale_fill_manual(values=c("#841108","#16a4e9","#a4a42a","#eb96ed","grey"),name="category") + 
  theme_bw() +
  opts(
    axis.text.x=theme_text(angle=-90,hjust=0),
    axis.line = theme_segment(colour = "black"),
    panel.grid.major = theme_blank(),
    panel.grid.minor = theme_blank(),
    panel.border = theme_blank()) +
  geom_vline(xintercept = 0)

When I use the transform to order the data frame, I get warnings and no ordering/sorting is performed. What I really would like is to sort such that bars for each category are grouped together(and in a decreasing order) along the x-axis. ( all the brown bars together, light-blue together and in 'hierarchical way' and so forth.)

How can I achieve that? Do i need multiple ordering? any idea?

Answer 1

I'm not entirely sure what ordering you actually want, but you might try something like this:

ex1.dta2 <- transform(ex1.dta,domain=reorder(domain,category,FUN = function(x){ min(as.numeric(x)) }))

The result will depend on how the levels of category are arranged, so you should adjust that if this isn't the exact ordering you want. In this case, I get the following graph:

What's going on here is that factors are stored internally as integer codes and set of labels. So to reorder based on the factor category I simply passed an anonymous function that converts to the integer codes, and then selects the minimum.