gistfile1.txt

measure <- structure(list(age = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L, 
4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L), .Label = c("7-yrs", "11-yrs", 
"15-yrs", "21-yrs"), class = "factor"), trt = structure(c(2L, 
2L, 2L, 2L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L), .Label = c("alternation", 
"repetition"), class = "factor"), value = c(814, 500, 424, 394, 
967, 574, 472, 446, 10, 6, 6, 4, 13, 7, 6, 3), variable = c("rt", 
"rt", "rt", "rt", "rt", "rt", "rt", "rt", "error", "error", "error", 
"error", "error", "error", "error", "error")), .Names = c("age", 
"trt", "value", "variable"), row.names = c(NA, 16L), class = "data.frame")
plot <- ggplot(measure, aes(age, value, colour = trt, fill = trt)) + 
  facet_grid(variable ~ . , scale = "free")
  
plot + geom_bar(position = "dodge")
plot + geom_line(aes(group = trt)) + geom_point()

# It's then just a matter of combining the two:
plot + 
  geom_bar(position = "dodge", subset = variable == "rt") + 
  geom_line(aes(group = trt), subset =  variable == "error")