Visualize events on a timeline with ggplot

Question

Goal

I like to visualize at which positions an event occurred. The data contains a simple counter (x) ranging from 1 to n() and a column hit which is either x when the event occurred or NA otherwise.

Data

library(dplyr)
library(ggplot2)
set.seed(6102023)
dat <- tibble(x = 1:5000) %>%
  mutate(hit = if_else(x %in% sample(n(), round(.2 * n())), "x", NA_character_))

Plot

ggplot(dat) +
  geom_text(aes(x = x, y = 1, label = if_else(is.na(hit), "", "|"))) +
  theme_minimal()

I am not happy with this visualization:

1. Although there was an event in only 20% of the cases, the timeline looks very dense giving the visual impression that there were by far more events.
2. We are wasting a lot of white space.

So I would need a crisper visualization which helps me to judge whether the events were distributed randomly or whether there was any sort of pattern.

Answer 1

Here's an attempt, with alpha and geom_segment:

ggplot(na.omit(dat)) +
  geom_segment(aes(x = x, xend = x, y = 0, yend = 1), color = "red", alpha = .1) +
  theme_minimal() +
  theme(axis.title.y=element_blank(),
        axis.text.y=element_blank(), 
        axis.ticks.y=element_blank())

---

An other option could be to use geom_histogram with the share of events per bin; binwidth controls the width of the bin along the x axis. With this method, you see clearly that each bin of 100 observations has

ggplot(na.omit(dat)) + aes(x = x) +
  geom_histogram(aes(y = after_stat(count / sum(count))), binwidth = 100, fill = "white", color = "black") +
  scale_y_continuous(labels = scales::percent_format()) + 
  theme_minimal()