How do I line up my error bars with my bars in ggplot?

Question

I'm creating a bar chart with a pattern for a subset of the bars, and I want to add error bars.

However, I'm having trouble lining up the error bars with with the bar charts—I want to have them appear centered on each bar. How do I do this? Moreover, the legend currently does not clearly distinguish the striped and non-striped bars as corresponding to not treated and treated groups.

Finally, I'd like to create version of this plot which stacks adjacent bars (ie bars within each facet_grid)—any tips on how to do that would be much appreciated.

The code I'm using is:

library(ggplot2)
library(tidyverse)
library(ggpattern)

models = c("a", "b")
task = c("1","2")
ratios = c(0.3, 0.4)
standard_errors = c(0.02, 0.02)

ymax = ratios + standard_errors
ymin = ratios - standard_errors

colors = c("#F39B7FFF", "#8491B4FF")

df <- data.frame(task = task, ratios = ratios)
df <- df %>% mutate(filler = 1-ratios)
df <- df %>% gather(key = "obs", value = "ratios", -1)
df$upper <- df$ratios + c(standard_errors,standard_errors)
df$models <- c(models,models)
df$lower <- df$ratios - c(standard_errors,standard_errors)
df$col <- c(colors,colors)
df$group <- paste(df$task, df$models, sep="-")
df$treated <- "yes"
df[df$ratios<0.5,]$treated = "no"

p <- ggplot(df, aes(x = group, y = ratios, fill = col, ymin = lower, ymax = upper)) + 
  stat_summary(aes(pattern=treated),
               fun = "mean", position=position_dodge(), 
               geom = "bar_pattern", pattern_fill="black", colour="black") +
        geom_errorbar(aes(ymin = lower, ymax = upper), width = 0.2, position=position_dodge(0.9)) +
        scale_pattern_manual(values=c("none", "stripe"))+ #edited part
        facet_grid(.~task, 
             scales = "free_x", # Let the x axis vary across facets.
             space = "free_x",  # Let the width of facets vary and force all bars to have the same width.
             switch = "x") + guides(colour = guide_legend(nrow = 1)) +
      guides(fill = "none")
p

Answer 1

Here is an option

df %>%
    ggplot(aes(x = models, y = ratios)) +
    geom_col_pattern(
        aes(fill = col, pattern = treated), 
        pattern_fill = "black",
        colour = "black",
        pattern_key_scale_factor = 0.2,
        position = position_dodge()) + 
    geom_errorbar(
         aes(ymin = lower, ymax = upper, group = interaction(task, treated)), 
         width = 0.2,
         position = position_dodge(0.9)) +
    facet_grid(~ task, scales = "free_x") +
    scale_pattern_manual(values = c("none", "stripe")) + 
    scale_fill_identity()

A few comments:

• I don't understand the point of creating group . IMO this is unnecessary. TBH, I also don't understand the point of models and task : if task = "1" then models = "a"; if task = "2" then models = "b"; so task and models are redundant as they encode the same thing (whether you call it "1"/"2" or "a"/"b").
• The reason why you (originally) didn't see a pattern in the legend is because of the scale factor in the legend key. As per ?scale_col_pattern , you can adjust this with the pattern_key_scale_factor parameter. Here, I've chosen pattern_key_scale_factor = 0.2 but you may want to play with different values.
• The reason why the error bars didn't align with the dodged bars was because geom_errorbar didn't know that there are different task - treated combinations. We can fix this by explicitly defining a group aesthetic given by the combination of task & treated values. The reason why you don't need this in geom_col_pattern is because you already allow for different treated values through the pattern aesthetic.
• You want to use scale_fill_identity() if you already have actual colour values defined in the data.frame .