How to stack scatterplot in ggplot2

Question

I am trying to create scatterplots in R using ggplot2 to visualize populations over time. 

My data set looks like the following:

sampling_period     cage     total_1    total_2     total_3
              4        y          34         95          12
              4        n          89         12          13
              5        n          23         10           2

I have been making individual scatterplots for the variables total_1, total_2, and total_3 with the following code:

qplot(data=BLPcaged, x=sampling_period, y=total_1, color=cage_or_control)
qplot(data=BLPcaged, x=sampling_period, y=total_2, color=cage_or_control)
qplot(data=BLPcaged, x=sampling_period, y=total_3, color=cage_or_control)

How to create a scatterplot that contains the information about all three populations over time?

I want the final product to be composed of three scatterplots one on top of each other and have the same scale for the axes. 

I know that I can use facet to make different plots for the levels of a factor, but can it also be used to create different plots for different variables?

Answer 1

Use melt() to reshape your data with total as a factor that you can facet on:

BLPcaged = data.frame(sampling_period=c(4,4,5),
                      cage=c('y','n','n'),
                      total_1=c(34,89,23),
                      total_2=c(95,12,10),
                      total_3=c(12,13,2))

library(reshape2)
BLPcaged.melted = melt(BLPcaged,
                       id.vars=c('sampling_period','cage'),
                       variable.name='total')

So now BLPcaged.melted looks like this:

  sampling_period cage   total value
1               4    y total_1    34
2               4    n total_1    89
3               5    n total_1    23
4               4    y total_2    95
5               4    n total_2    12
6               5    n total_2    10
7               4    y total_3    12
8               4    n total_3    13
9               5    n total_3     2

You can then facet this by total:

ggplot(BLPcaged.melted, aes(sampling_period, value, color=cage)) + 
geom_point() + 
facet_grid(total~.)