R: overlying trajectory plot and scatter plot

Question

I'm working with ggplot2 and trajectory plots, plots whom are like scatter plots, but with lines that connect points due a specific rule.
My goal is to overlay a trajectory plot with a scatter plot, and each of them has different data. First of all, the data:

# first dataset
ideal <- data.frame(ideal=c('a','b')
                ,x_i=c(0.3,0.8)
                ,y_i=c(0.11, 0.23))

# second dataset
calculated <- data.frame(calc = c("alpha","alpha","alpha")
                     ,time = c(1,2,3)
                     ,x_c = c(0.1,0.9,0.3)
                     ,y_c = c(0.01,0.26,0.17)
                     )

Creating a scatter plot with the first one is easy:

library(ggplot2)
ggplot(calculated, aes(x=x_c, y=y_c)) + geom_point()

After that, I created the trajectory plot, using this helpful link :

library(grid)
library(data.table)

qplot(x_c, y_c, data = calculated, color = calc, group = calc)+ 
  geom_path (linetype=1, size=0.5, arrow=arrow(angle=15, type="closed"))+ 
  geom_point (data = calculated, colour = "red")+
  geom_point (shape=19, size=5, fill="black")

With this result:

How can I overlay the ideal data to this trajectory plot (without trajectory of course, they should be only points)?
Thanks in advance!

Answer 1

qplot isn't usually recommended. Here's how you could plot the two dataframes. However, ggplot might work better for you if the dataframes were merged, and you had an x and y column, with an additional method column containing with calculated or ideal .

library(ggplot2)

ideal <- data.frame(ideal=c('a','b')
                    ,x_i=c(0.3,0.8)
                    ,y_i=c(0.11, 0.23)
                    )

# second dataset
calculated <- data.frame(calc = c("alpha","alpha","alpha")
                         ,time = c(1,2,3)
                         ,x_c = c(0.1,0.9,0.3)
                         ,y_c = c(0.01,0.26,0.17)
                         )

ggplot(aes(x_c, y_c, color = "calculated"), data = calculated) + 
  geom_point( size = 5) +
  geom_path (linetype=1, size=0.5, arrow = arrow(angle=15, type="closed"))+ 
  geom_point(aes(x_i, y_i, color = "ideal"), data = ideal, size = 5) + 
  labs(x = "x", y = "y", color = "method")