如何在ggplot2 heatmap中的特定区域添加边界框？

Question

我使用here中的示例。我的问题是如何在此热图中添加特定的边界框，例如在左上角的四个图块中添加一个红线框？

require(ggplot2)
require(reshape)
require(scales)

mydf <- data.frame(industry = c('all industries','steel','cars'), 
    'all regions' = c(250,150,100), americas = c(150,90,60), 
     europe = c(150,60,40), check.names = FALSE)
mydf

mymelt <- melt(mydf, id.var = c('industry'))
mymelt

ggplot(mymelt, aes(x = industry, y = variable, fill = value)) +
    geom_tile() + geom_text(aes(fill = mymelt$value, label = mymelt$value))

Answer 1

快速而肮脏（一些硬编码）的可能性是使用geom_rect，其中位置由要与框绑定的x和y变量的级别的数值给出，加/减抵消。

ggplot(mymelt, aes(x = industry, y = variable, fill = value, label = value)) +
  geom_tile() +
  geom_text() +
  geom_rect(aes(xmin = 1 - 0.5, xmax = 2 + 0.5, ymin = 2 - 0.5, ymax = 3 + 0.5),
               fill = "transparent", color = "red", size = 1.5)

硬编码较少的版本：

# convert x and y variables to factors
ind <- as.factor(mymelt$industry)
vars <- as.factor(mymelt$variable)

# numeric version of the levels to be bound by a box
xmin <- unique(as.numeric(ind[ind == "all industries"]))
xmax <- unique(as.numeric(ind[ind == "cars"]))

ymin <- unique(as.numeric(vars[vars == "americas"]))
ymax <- unique(as.numeric(vars[vars == "europe"]))

# set offset
offset <- 0.5

ggplot(mymelt, aes(x = industry, y = variable, fill = value, label = value)) +
  geom_tile() +
  geom_text() +
  geom_rect(aes(xmin = xmin - offset,
                xmax = xmax + offset,
                ymin = ymin - offset,
                ymax = ymax + offset),
            fill = "transparent", color = "red", size = 1.5)