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rggplot2

r - ggplot2 geom_errorbar with solid whisker lines and position dodged

I am trying to create a line plot and have one of the groups use a dotted line type. Unfortunately the whiskers can be hard to see with dotted lines so I am trying to add solid lines for the whiskers.

I tried to follow the suggested solution in this questions.

ggplot2 geom_errorbar with different linetype but with solid whiskers

Unfortunately something weird is happening when also using position dodge.

library(ggplot2)
library(dplyr)

dat <- data.frame(cohort = rep(c("Placebo", "Trt 1", "Trt 2"), times = 3),
                  visit = c(rep("Baseline", times = 3), rep("Time 2", times = 3), rep("Time 3", times = 3)),
                  visitnum = c(rep(1, times = 3), rep(2, times = 3), rep(3, times = 3)),
                  mean = rnorm(9)
                  ) %>% 
  mutate(lower = mean - 1,
         upper = mean + 1)

dodge <- position_dodge2(.25)

dat %>% ggplot(aes(x = visitnum, y = mean, color = cohort, group = cohort, linetype = cohort)) +
  geom_line(position = dodge) +
  geom_point(position = dodge) +
  geom_linerange(aes(ymin = lower, ymax = upper),
                 position = dodge) +
  geom_segment(aes(x = visitnum-.1, xend = visitnum+.1, y = lower, yend = lower), position = dodge, linetype = "solid") +
  geom_segment(aes(x = visitnum-.1, xend = visitnum+.1, y = upper, yend = upper), position = dodge, linetype = "solid") +
  
  scale_linetype_manual(values = c("solid", "solid", "dotted")) +
  
  scale_x_continuous(breaks = unique(dat$visitnum), labels = unique(dat$visit))

The lines created by geom_segment seem to be right adjusted.

plot

Any help would be greatly appreciated.

Solution

  • One option would be to "manually" dodge the whiskers aka segments by computing the x and xend positions yourself instead of relying on position_dodge:

    library(ggplot2)

set.seed(123)

dw <- .45
dodge <- position_dodge(dw)

dat$cohort_num <- as.numeric(factor(dat$cohort))
dat |> ggplot(aes(x = visitnum, y = mean, color = cohort, group = cohort, linetype = cohort)) +
  geom_line(position = dodge) +
  geom_point(position = dodge) +
  geom_linerange(aes(ymin = lower, ymax = upper),
    position = dodge
  ) +
  geom_segment(
    aes(
      x = visitnum - .05 + dw / 3 * scales::rescale(cohort_num, to = c(-1, 1)),
      xend = visitnum + .05 + dw / 3 * scales::rescale(cohort_num, to = c(-1, 1)),
      y = lower, yend = lower
    ),
    linetype = "solid"
  ) +
  geom_segment(
    aes(
      x = visitnum - .05 + dw / 3 * scales::rescale(cohort_num, to = c(-1, 1)),
      xend = visitnum + .05 + dw / 3 * scales::rescale(cohort_num, to = c(-1, 1)),
      y = upper, yend = upper
    ),
    linetype = "solid"
  ) +
  scale_linetype_manual(values = c("solid", "solid", "dotted")) +
  scale_x_continuous(breaks = unique(dat$visitnum), labels = unique(dat$visit))