r - 在 ggplot() 中将误差线放置在列中心时出现问题

Question

我的条形图有问题 - 误差线仅出现在分组变量的列的角上，而不是以集中的方式出现在它们上。我使用的代码是这样的:

a <- data.frame (Cond = c("In", "In", "Out", "Out"),
                Temp = c("Hot", "Cool", "Hot", "Cool"),
                Score = c(.03, -.15, 0.84, 0.25),
                SE = c(.02, .08, .14, .12))
a.bar <- ggplot (data = a, aes(x = Cond, y = Score, fill = Temp)) +
            theme_bw() + theme(panel.grid = element_blank ()) +
            coord_cartesian (ylim = c(-0.5, 1)) + 
            geom_bar (aes(fill = Temp), stat = "identity", position = "dodge", width = .5) +
            geom_errorbar (aes(ymin = Score - SE, ymax = Score + SE, group = Cond), position = position_dodge(.9), width = .08) +
            labs(y = "Scores" , x = "Cond") +
            scale_y_continuous (breaks = pretty_breaks(n=8)) +
            theme(legend.title = element_blank()) +
            theme(legend.position = "right")

我尝试过的替代代码也无法工作，包括将“show.legend = FALSE”添加到geom_bar();添加“facet_wrap(~Cond)”plot.a；并在 ggplot(aes()) 中引入“fill = Temp”。最接近的解决方案是当我将position_dodge()参数更改为:

geom_bar (aes(fill = Temp), stat = "identity", position = position_dodge(width = .5)) +
geom_errorbar (aes(ymin = Score - SE, ymax = Score + SE, group = Cond), position = position_dodge(.5), width = .08) +

(其余代码保持不变)。这将误差线移向列的中心，同时也将列移向彼此，最终使它们重叠(参见附图)。

我非常感谢对此的帮助。

谢谢!

Answer 1

问得好。一些评论:

1. 一般来说，最好在原始 ggplot() 调用中设置所有美学，并且仅在单独的 geom_xyz 中需要时才使用不同的美学覆盖它们() 调用。在您的代码中，您设置了两次填充美学，一次在 ggplot 中，一次在 geom_bar 中。您还可以在 geom_errorbar() 中设置组美感。我不认为这些事情是最终的问题，但它们确实使调试代码变得更加困难。

2. 主要问题是 geom_bar 中的 width 参数必须与 geom_errorbar 中的 position_dodge() 参数相匹配。所以如果你有

   # ...
   geom_bar(stat = "identity", position = "dodge", width = 0.5)
   # ...
   

   然后你必须确保你的geom_errorbar()看起来像

   # ...
   geom_errorbar(width = .08, position = position_dodge(0.5)) 
   # ...
   

把它们放在一起:

require(ggplot2)
require(scales)

# define data
a <- data.frame (Cond = c("In", "In", "Out", "Out"),
                Temp = c("Hot", "Cool", "Hot", "Cool"),
                Score = c(.03, -.15, 0.84, 0.25),
                SE = c(.02, .08, .14, .12))

# return plot with everything except error bars
a.bar <- ggplot (data = a, aes(x = Cond, 
                               y = Score, 
                               fill = Temp,
                               ymin = Score - SE,
                               ymax = Score + SE)) +
            theme_bw() + 
            theme(panel.grid = element_blank ()) +
            coord_cartesian(ylim = c(-0.5, 1)) + 
            # manually setting the width means we will have to tell geom_errorbar() about the new width
            geom_bar(stat = "identity", position = "dodge", width = 0.5) + 
            labs(y = "Scores", x = "Cond") +
            scale_y_continuous(breaks = pretty_breaks(n = 8)) +
            theme(legend.title = element_blank()) +
            theme(legend.position = "right")

# show plot w/ errorbars, note that argument to position_dodge is same as width supplied above
a.bar + geom_errorbar(width = .08, position = position_dodge(0.5)) 

# save results
ggsave('SO_35424162.png')