How do I connect geom_points for ID when col is not ID in ggplot?

February 1, 2023

I’m trying to make a ggplot (in Shiny): I have concentration-time data that I want to visualize. There’s an option for the user to colour different groups in the plot, for example, Species, Antibodies, etc. However, I also want them to see the different concentration-time graphs for every ID, so what I actually want to achieve is that the data is colored by Species but the data points for each individual are connected.

I can give you an example data set:

dfc <- data.frame(
  ID = c(1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4),
  Conc = c(4, 3.5, 3, 1, 5, 4.5, 4, 2, 3, 2.5, 2, 1, 6, 5.5, 5, 4),
  Time = c(0.15, 1, 2, 3, 0.15, 1, 2, 3, 0.15, 1, 2, 3, 0.15, 1, 2, 3),
  Species= c("Monkey", "Monkey", "Monkey", "Monkey", "Monkey", "Monkey", "Monkey", "Monkey", "Mouse", "Mouse","Mouse","Mouse","Mouse","Mouse","Mouse","Mouse"))

I’m working on a Shiny app that is very big right now, so I won’t bother you with all code, but that’s just something easy right now. What I tried is this:

plot <- ggplot() + geom_point(dfc, mapping=aes(Time, Conc, col = Species)) + geom_line(dfc, mapping=aes("ID"))
plot

Obviously, this doesn’t work and I’m also not sure how to do this. I hope someone can help me with this because I feel like the answer is simple, but I can’t figure it out right now.

>Solution :

You could connect your points using group in your geom_line by ID like this:

library(ggplot2)
plot <- ggplot() + 
  geom_line(dfc, mapping=aes(x = Time, y = Conc, group = ID)) +
  geom_point(dfc, mapping=aes(Time, Conc, col = Species)) 
plot