Deleting or blanking a facet cell in ggplot2

Suppose you have some ragged data.

set.seed(20220121)
library(tidyverse)
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data <- tibble(
  id = letters[1:14],
  group = rep(c("g1", "g2", "g3"), times = c(5, 4, 5)),
  data = lapply(1:14, function(x) {
    # just making some data
    n_points <- sample(c(2:5), size = 1) 
    ages <- sort(sample(c(10:24), size = n_points))
    data.frame(age = ages, score = rbeta(n_points, 1, 4))
  })
) %>% 
  tidyr::unnest(data)

ggplot(data, aes(x = age, y = score)) + 
  geom_point() + 
  geom_line(aes(color = group)) + 
  facet_wrap("id", ncol = 5)

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We would like to have one row per group. So we actually would want four panels on the middle row. If we add an extra panel to fill that space and then remove it, we can achieve this goal.

First add the dummy panel.

data <- data %>% 
  tibble::add_row(id = "i2", group = "g2", age = median(data$age), score = 0) %>% 
  # two points so that geom_line() doesn't warn
  tibble::add_row(id = "i2", group = "g2", age = median(data$age), score = 0)

ggplot(data, aes(x = age, y = score)) + 
  geom_point(na.rm = TRUE) + 
  geom_line(aes(color = group), na.rm = TRUE) + 
  facet_wrap("id", ncol = 5) 

center

2026 note: This broke over time. My overly complicated approach was to manually delete the grob using the following. Finding the pattern name is very tedious because you basically have to guess the strip and panel numbers.

p <- last_plot()
g <- ggplotGrob(p)
# guess and check
pattern <- "panel-4-3|strip-t-5-2"
to_drop <- str_which(g$layout$name, pattern)
to_keep_names <- str_subset(g$layout$name, pattern, negate = TRUE)
# delete grob data, clean up layout table
g$grobs[to_drop] <- NULL
g$layout <- g$layout[g$layout$name %in% to_keep_names, ]
grid::grid.newpage()
grid::grid.draw(g)

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Although I am going to give better solution, I did write this entry precisely to have this code here for my reference.

A better approach is to blank the cell with a ribbon. We have to eliminate strip titles from the theme for this approach to work.

ggplot(data, aes(x = age, y = score)) + 
  geom_point(na.rm = TRUE) + 
  geom_line(aes(color = group), na.rm = TRUE) + 
  geom_ribbon(
    aes(ymin = -Inf, ymax = Inf),
    data = tibble(
      id = "i2", 
      age = c(-Inf, Inf), 
      group = "g2", 
      score = NA_real_
    ),
    fill = "white",
    color = "white"
  ) +
  facet_wrap("id", ncol = 5) +
  theme(strip.text.x = element_blank())

center

Brenton on Twitter suggested numbering IDs within groups and using facet_grid(). That works, and it also can give labeled rows.

data <- data %>% 
  group_by(group) %>% 
  mutate(col_num = match(id, unique(id))) %>% 
  ungroup()

ggplot(data, aes(x = age, y = score)) + 
  geom_point(na.rm = TRUE) + 
  geom_line(aes(color = group), na.rm = TRUE) + 
  geom_ribbon(
    aes(ymin = -Inf, ymax = Inf),
    data = tibble(
      col_num = 5,
      age = c(-Inf, Inf), 
      group = "g2", 
      score = NA_real_
    ),
    fill = "white",
    color = "white"
  ) +
  facet_grid(group ~ col_num) +
  theme(strip.text.x = element_blank())

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