如何调整用stat_summary_bin创建的错误栏的宽度？

Question

我用下面的代码创建了一个分组的条形图。我想将错误栏的宽度调整为当前宽度的一半。但是，width = 0.5对结果没有影响。我应该怎么做？

library(ggplot2) 
# ggplot2_2.2.1 

df <- iris 
set.seed(1) 
df$group <- sample(c('I', 'II'), nrow(df), replace = T) 

ggplot(df, aes(x = group, y = Sepal.Width, fill = Species)) + 
    stat_summary_bin(fun.data = "mean_cl_normal", 
        geom = 'bar', position = 'dodge') + 
    stat_summary_bin(fun.data = "mean_cl_normal", 
        geom = 'errorbar', position = 'dodge', width = 0.5) 

Answer 1

# ?geom_errorbar, see bottom 
# Because the bars and errorbars have different widths 
# we need to specify how wide the objects we are dodging are 

dodge <- position_dodge(width = 0.9) 

ggplot(df, aes(x = group, y = Sepal.Width, fill = Species)) + 
stat_summary(fun.data = "mean_cl_normal", geom = 'bar', position = dodge) + 
stat_summary(fun.data = "mean_cl_normal", geom = 'errorbar', position = dodge, width = 0.5)