Aligning a geom_text layer vertically on a bar chart

Question

I currently have the geom_text set to the center of the bar chart...

library(dplyr)
library(ggplot2)

enroll_bar <- enroll_cohort %>%
    filter(chrt_grad != 2013) %>%
    mutate(college_enrolled = factor(college_enrolled),
           chrt_grad = factor(chrt_grad)) %>%
    mutate(label_height = cumsum(n)) %>%
    ggplot() +
    geom_col(mapping = aes(x = chrt_grad,
                           y = n,
                           fill = fct_rev(college_enrolled))) +
    geom_text(aes(x = chrt_grad, y = label_height, label = n), color = "white",
              position = position_stack(vjust = 0.5)) +
    scale_y_continuous(expand = expansion(mult = c(0, 0.1))) +
    labs(x = NULL, y = NULL) +
    scale_fill_manual(labels = c("Enrolled", "Not Enrolled"),
                      values = c("#00aeff", "#005488"))

How do I align the text vertically, so the geom_text layer is set at the same y-axis position for each bar? Also, is there a way to do this so the text is always aligned no matter the scale of the y-axis because this is a parameterized report and the y-axis values change with each report?

Answer 1

You can set a uniform label height for each group using if_else (or case_when for >2 groups). For a single plot, you can simply set a value, e.g., label_height = if_else(college_enrolled == "Enrolled", 20000, 3000). To make the relative height consistent across multiple plots, you can instead set label_height as a proportion of the y-axis range:

library(tidyverse)

# make a fake dataset
enroll_cohort <- expand_grid(
    chrt_grad = factor(2014:2021),
    college_enrolled = factor(c("Enrolled", "Not Enrolled")),
  ) %>%
  mutate(
    n = sample(18000:26000, 16),
    n = if_else(college_enrolled == "Enrolled", n, as.integer(n / 3))
  )

enroll_bar <- enroll_cohort %>% 
  group_by(chrt_grad) %>%            # find each bar's height by summing up `n`
  mutate(bar_height = sum(n)) %>%    # within each year
  ungroup() %>%
  mutate(label_height = if_else(
    college_enrolled == "Enrolled", 
    max(bar_height) * .6,            # axis height is max() of bar heights;
    max(bar_height) * .1             # set label_height as % of axis height
  )) %>%
  ggplot() +
  geom_col(aes(x = chrt_grad, y = n, fill = college_enrolled), color = NA) +
  geom_text(
    aes(x = chrt_grad, y = label_height, label = n), 
    color = "white"
  ) +
  scale_y_continuous(expand = expansion(mult = c(0, 0.1))) +
  labs(x = NULL, y = NULL) +
  scale_fill_manual(values = c("#00aeff", "#005488"))

If we generate another dataset with a different range of n values -- e.g., ~1200 - ~2000 -- the text labels stay at the same relative positions: