如何从图例中删除已使用的值？ [英] How can I drop a used value from the legend?

问题描述

简而言之

我知道scale_*_*(drop = TRUE)可用于从图例中删除空因素级别。也许与直觉相反的是，我正在尝试从绘图中删除已用级别。

正如您可能已经猜到的，这是一个有点老套的用例：我在geom_bar中使用不可见条来抵消"浮动"Likert响应的可视化效果。我对帧挑战或解决此问题的其他方法不感兴趣，我特别询问如何从图例中删除使用过的级别。

用例和示例

下面的代码重现了我的可视化的一个非常简单的版本。它工作得很好，但图例离中心的距离很小(这在真正的可视化中更值得注意)。我想把"看不见"的水平降下来来呈现这一点。我知道我可以使用数字参数legend.position将整个事情重新居中，但这很麻烦，而且不能一概而论。

## libraries ---
require(ggplot2)
#> Loading required package: ggplot2
require(dplyr)
#> Loading required package: dplyr
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union

## data ---
plotData <- tibble(label = 
                     factor(c("", "strawberries", "blueberries", "", "strawberries", "blueberries"),
                             levels = c("strawberries", "blueberries", ""), ordered = TRUE),
                   value = c(30, 40, 20, 15, 30, 15),
                   bowl = factor(c("bowl1", "bowl1", "bowl1", "bowl2", "bowl2", "bowl2"))) 

## plot ---

### Specs for the legend
legendSpecs <- guide_legend(nrow = 1, label.position = "bottom",
                            reverse = TRUE, title = NULL)
### desired plot
ggplot(plotData, aes(x = value, y = bowl,
                     fill = label, colour = label)) +
  geom_bar(stat = "identity", position = "stack") +
  scale_fill_manual(values = c("blue", "red", NA), guide = legendSpecs) +
  scale_colour_manual(values = c("black",  "black", NA), guide = legendSpecs) +
  theme_minimal() +
  theme(legend.position = "bottom")

演示我要删除的图例中的小偏移量：

### demonstrating legend offset
ggplot(plotData, aes(x = value, y = bowl,
                     fill = label, colour = label)) +
  geom_bar(stat = "identity", position = "stack") +
  scale_fill_manual(values = c("blue", "red", NA), guide = legendSpecs) +
  scale_colour_manual(values = c("black",  "black", "black"), guide = legendSpecs) +
  theme_minimal() +
  theme(legend.position = "bottom")

^{由reprex package(v2.0.0)}在2021-06-30创建

推荐答案

这可以通过将刻度的breaks设置为仅包括所需类别来实现：

## libraries ---
require(ggplot2)
require(dplyr)

## data ---
plotData <- tibble(label = 
                     factor(c("", "strawberries", "blueberries", "", "strawberries", "blueberries"),
                            levels = c("strawberries", "blueberries", ""), ordered = TRUE),
                   value = c(30, 40, 20, 15, 30, 15),
                   bowl = factor(c("bowl1", "bowl1", "bowl1", "bowl2", "bowl2", "bowl2"))) 

## plot ---

### Specs for the legend
legendSpecs <- guide_legend(nrow = 1, label.position = "bottom",
                            reverse = TRUE, title = NULL)
### desired plot
ggplot(plotData, aes(x = value, y = bowl,
                     fill = label, colour = label)) +
  geom_bar(stat = "identity", position = "stack") +
  scale_fill_manual(values = c("blue", "red", NA), na.value = NA,
                    guide = legendSpecs, breaks = c("blueberries", "strawberries"))  +
  scale_colour_manual(values = c("black",  "black", NA), , na.value = NA, 
                      guide = legendSpecs, 
                      breaks = c("blueberries", "strawberries")) +
  theme_minimal() +
  theme(legend.position = "bottom")

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