library(tidyverse)

xVals <- function(n, center, width) {
  seq(from = center - width, to = center + width, length.out = n)
}
width <- 0.3
survey <- tigerstats::m111survey
gms <-
  survey %>%
  group_by(seat) %>%
  summarize(groupMean = mean(fastest), n = n()) %>%
  mutate(grpNumber = as.numeric(seat)) %>%
  mutate(xStart = grpNumber - width,
         xEnd = grpNumber + width)

xs <- c(xVals(gms$n[1], 1, width),
        xVals(gms$n[2], 2, width),
        xVals(gms$n[3], 3, width))

survey <-
  survey %>%
  inner_join(gms, by = "seat") %>%
  mutate(grandMean = mean(fastest)) %>%
  arrange(seat) %>%
  mutate(xs = xs)

# SSE
ggplot(survey, aes(x = xs, y = fastest)) +
  geom_point() +
  geom_segment(aes(x = xs, y = fastest, xend = xs, yend = groupMean)) +
  geom_segment(gms,
               mapping = aes(x = xStart, xend = xEnd, y = groupMean, yend = groupMean))