如何从图例中删除已使用的值？

In Brief

我知道scale_*_*(drop = TRUE)可用于从图例中删除空因子水平。也许违反直觉，我试图放弃used情节的水平。

正如您可能已经猜到的，这是一个稍微有点 hack 的用例：我使用隐形条geom_bar抵消“浮动”的李克特反应可视化。我是not对框架挑战或解决此问题的替代方法感兴趣，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，但图例从中心稍微偏移（这在“真实”可视化中更明显）。我想放弃“看不见”的层面来呈现这一点。我知道我可以使用数字参数legend.position重新集中整个事情的中心，但这是繁琐且不可概括的。

## 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")

展示我试图消除的图例中的小偏移：

### 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")

^{Created on 2021-06-30 by the reprex package https://reprex.tidyverse.org (v2.0.0)}

这可以通过设置来实现breaks仅包含所需类别的量表：

## 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")