Using columns as factors for plotting in R

Question

I have a data frame that looks like this:

> head(DOData)
    Date        Site1 Site2  Site3   Site4  Site5  Months
1   1/1/2012    1.07  3.32   11.35   6.26   5.39   January
2   1/2/2012    1.24  3.08   10.69   6.57   6.59   January
3   1/3/2012    1.94  2.69   11.86   6.23   6.23   January
4   1/4/2012    0.81  3.50   11.47   4.67   5.94   January
5   1/5/2012    1.41  3.11   10.38   7.44   5.40   January
6   1/6/2012    2.73  3.28   11.11   6.15   6.22   January
.
.
.
361 12/26/2012  3.54  3.86   12.67   5.44   6.03   December
362 12/27/2012  2.05  3.42   10.27   6.05   7.10   December
363 12/28/2012  3.59  2.96   11.10   6.71   5.68   December
364 12/29/2012  1.81  3.57   11.20   7.20   7.71   December
365 12/30/2012  4.03  2.00   11.07   7.15   5.93   December
366 12/31/2012  1.93  2.03   11.90   6.06   8.46   December

i.e. a year's worth of data for 5 sites, with one row per day.

I'd like to create some ggplot2 boxplot's of data for individual months, using the five sites as factors. I suppose I could put all my data into a single column and then add a new column for the site name, but then I'd still need to somehow select the individual months. I wonder, do I really need to reorganize my data, or is there some way to use the columns as factors? Thanks for your help!

Answer 1

It will be much easier if you rearrange your data frame. This can be done with the reshape2 package:

library(reshape2)
DOData2 <- melt(DOData)

Now, the creation of the plot is straightforward:

library(ggplot2)
ggplot(DOData2) +
  geom_boxplot(aes(y = value, x = Months, colour = variable))