To do so, specify group attribute in aes() in ggplot2 expression. This would allow points connected in the subplots defined by facet_wrap() or facet_grid().
Working example:
dat <- data.frame(x = rep(1:3, 4),
y = c(1:12),
individual = factor(c(1,1,1, 2,2,2, 3,3,3, 4,4,4)),
type = factor(c(rep("A", 6), rep("B", 6)))
)
# without specifying group
dat %>% ggplot(aes(x = x, y = y)) +
geom_point() + facet_wrap(type ~ .) +
geom_line()
# specify "individual" as grouping variable
dat %>% ggplot(aes(x = x, y = y, group = individual)) +
geom_point() + facet_wrap(type ~ .) +
geom_line()
