Question

I am trying to plot some categorical data and this answer is very close to what I am trying to do, however in my case I have dates in the place of countries as seen in this example. How can I create the plot with the original row order from the data.frame? It appears that even though the factors are in the same order in dat and melt.data they are not ordered sequentially on the y axis in the plot.

Here is a reproducible example:

library(reshape)
library(ggplot2)

dat <- data.frame(dates=c("01/01/2002", "09/15/2003", "05/31/2012"), Germany = c(0,1,0), Italy = c(1,0,0))
melt.data<-melt(dat, id.vars="dates", variable_name="country")

qplot(data=melt.data,
      x=country,
      y=dates,
      fill=factor(value),
      geom="tile")

Answer 1

Your problem is that date is stored as a character string. See str(dat) for a structure of the data.

By adding

dat$dates <- as.Date(dat$dates,"%m/%d/%Y")

after loading dat, you can get the dates in the original order.