reordering_bar_chart

library(ggplot2)

dat <- data.frame(bars = rep(c("a","b","c","d"), each=3),
                  stacks = rep(c("a","b","c"), times=4),
                  value = c(20,60,20,10,70,20,70,10,20,40,40,20))

dat$stacks <- as.character(dat$stacks)

ggplot(data=dat, aes(x=bars, y=value, fill=stacks))+
  geom_bar(stat="identity")

correctorder <- c("c","b","a")

dat$stacks <- factor(dat$stacks, levels=correctorder)

ggplot(data=dat, aes(x=bars, y=value, fill=stacks))+
  geom_bar(stat="identity")