Making a stacked bar plot for multiple variables - ggplot2 in R

Question

I have some problems with making a stacked bar chart in ggplot2. I know how to make one with barplot(), but I wanted to use ggplot2 because it\'s very easy to make the bars

Answer 1

Excuse me for initiating a new answer while I really just want to add a comment on the beautiful solution provided by @Richie. I don't have the minimal points to post a comments, so here is my case:

The ... + geom_bar(position="fill") threw an error for my plotting, I'm using ggplot2 version 0.9.3.1. and reshape2 rather than reshape for the melting.

error_message:
*Mapping a variable to y and also using stat="bin".
  With stat="bin", it will attempt to set the y value to the count of cases in each group.
  This can result in unexpected behavior and will not be allowed in a future version of ggplot2.
  If you want y to represent counts of cases, use stat="bin" and don't map a variable to y.
  If you want y to represent values in the data, use stat="identity".
  See ?geom_bar for examples. (Deprecated; last used in version 0.9.2)
stat_bin: binwidth defaulted to range/30. Use 'binwidth = x' to adjust this.
Error in pmin(y, 0) : object 'y' not found*

So I changed it to geom_bar(stat='identity') and it works.