如何根据条形的填充暗度控制标签颜色？

Question

我有一个堆积的条形图，标有geom_text。为了增加标签的可见性，我想根据标签背景的“暗度”（即条形的填充色）将标签颜色设置为白色或黑色。因此，较深的条应带有白色标签，而较浅的条应带有黑色标签。

我从问题显示代码开始，该问题在ggplot2中的堆叠条形图上显示数据值，问题的答案R中是否有浅色或深色函数？。最重要的是，我想显示数据值的标签为“白色”或“黑色”，分别取决于堆叠的条形填充颜色是深色还是深色。

我做了两次尝试。第一个是函数的使用aes(colour=...)，geom_text但是这个函数失败了……为什么？

第二次尝试是使用函数scale_colour_manual。但是在这里，堆叠的条形线也使用黑色或白色切换设置“着色”。

library(ggplot2)
library(RColorBrewer)

Year      <- c(rep(c("2006-07", "2007-08", "2008-09", "2009-10"), each = 4))
Category  <- c(rep(c("A", "B", "C", "D"), times = 4))
Frequency <- c(168, 259, 226, 340, 216, 431, 319, 368, 423, 645, 234, 685, 166, 467, 274, 251)
Data      <- data.frame(Year, Category, Frequency)

isDark <- function(color) {
  (sum(grDevices::col2rgb(color) *c(299, 587,114))/1000 < 123)
}

## control the color assignments
paletteName <- 'Set1' # 'Dark2'
colorsPerCat <- brewer.pal(name=paletteName,n=4)
names(colorsPerCat) <- c("A", "B", "C", "D")

## First attempt
Data$LabelColor <- as.character(as.vector(sapply(unlist(colorsPerCat)[Data$Category], function(color) { if (isDark(color)) 'white' else 'black' })))
Data
p <- ggplot(Data, aes(x = Year, y = Frequency, fill = Category, label = Frequency)) +
  geom_bar(stat = "identity") +
  geom_text(aes(colour=LabelColor), size = 3, position = position_stack(vjust = 0.5)) +
  scale_fill_manual(values = colorsPerCat)
p

## Second attempt
labelColoursPerCat <- sapply(as.vector(colorsPerCat), function(color) { if (isDark(color)) 'white' else 'black' })
names(labelColoursPerCat) <- c("A", "B", "C", "D")
p <- ggplot(Data, aes(x = Year, y = Frequency, fill = Category, label = Frequency, colour = Category)) +
  geom_bar(stat = "identity") +
  geom_text(size = 3, position = position_stack(vjust = 0.5)) +
  scale_fill_manual(values = colorsPerCat) +
  scale_colour_manual(values = labelColoursPerCat)
p

Answer 1

通过调整geom_bar 颜色或尺寸来解决此问题的两种方法：

Data$LabelColor <- as.factor(Data$LabelColor)
p <- ggplot(Data, aes(x = Year, y = Frequency, fill = Category, label = Frequency, colour = LabelColor)) +
              geom_bar(stat = "identity", color = "black") +
              geom_text(size = 3, position = position_stack(vjust = 0.5)) +
              scale_fill_manual(values = colorsPerCat) +  
              scale_colour_manual(values = levels(Data$LabelColor)) +
              guides(colour = FALSE)

Data$LabelColor <- as.factor(Data$LabelColor)
p <- ggplot(Data, aes(x = Year, y = Frequency, fill = Category, label = Frequency, colour=LabelColor)) +
              geom_bar(stat = "identity", size = 0) +
              geom_text(size = 3, position = position_stack(vjust = 0.5)) +
              scale_colour_manual(values = levels(Data$LabelColor)) +
              scale_fill_manual(values = colorsPerCat) +  
              guides(colour = FALSE)