How subset a data frame by a factor and repeat a plot for each subset?

Question

I am new to R. Forgive me if this if this question has an obvious answer but I\'ve not been able to find a solution. I have experience with SAS and may just be thinking of t

Answer 1

A few years ago, I wanted to do something similar - plot individual trajectories for ~2500 participants with 1-7 measurements each. I did it like this, using plyr and ggplot2:

library(plyr)
library(ggplot2)

d_ply(dat, .var = "participant_id", .fun = function(x) {

    # Generate the desired plot
    ggplot(x, aes(x = phase, y = result)) +
        geom_point() +
        geom_line()

    # Save it to a file named after the participant
    # Putting it in a subdirectory is prudent
    ggsave(file.path("plots", paste0(x$participant_id, ".png")))

})

A little slow, but it worked. If you want to get a sense of all participants' trajectories in one plot (like your second example - aka the spaghetti plot), you can tweak the transparency of the lines (forget coloring them, though):

ggplot(data = dat, aes(x = phase, y = result, group = participant_id)) + 
    geom_line(alpha = 0.3)