使用带有 geom_label_repel 的 plotmath 在标签中添加下标

Question

我正在尝试在我的geom_label 中添加下标。例如

缅因州
A_po (km/h) = 9
Q_t (m/s) = 90

我知道使用[x] 来获取下标，但是当我想（部分）从列中获取标签值时，我不确定如何实现。我尝试使用 tidyeval (!!) 无济于事。即使只是简单地更改 parse = T 也会给我带来错误。我可能忽略了一些基本的东西，但是在阅读了这个帖子using plotmath in ggrepel labels之后，我不确定它是否像我想象的那么简单。

这是我目前所拥有的。我提供了我使用的包和数据，以及数据清理/准备步骤。最后，我展示了用于创建“初步”图的代码。

library(tidyverse)
library(stringr)
library(usmap)
library(ggrepel)
library(rlang)

read.table(text = "State     Apo    Qt
NJ  1     10
MO  2     20
SD  3     30
NY  4     40
FL  5     50
OK  6     60
NE  7     70
KY  8     80
ME  9     90
CA  10  100
NC  11  110
MA  12  120
CT  13  140", header = T, stringsAsFactor = F) -> ex1

# get the states full names
region <- state.name[match(ex1$State,state.abb)]
region <- str_to_title(region)

# US map data (50 States)
us1 <- usmap::us_map()

# adding full names to the dataset
ex_df <- cbind(region = region, ex1)

# adding dataset values to the map data (only states with data)
us_val1 <- left_join(ex_df, us1, by = c("region" = "full")) 

# full map dataset joined by ex1 dataset to draw the map
us_map1 <- left_join(us1, ex_df, by = c("full" ="region")) %>% 
           mutate(qQt = replace_na(Qt, 0))

# creating a dataset with centroids of the states (only the ones in ex1)
us_centroids1 <- 
  us_val1 %>%
  group_by(region) %>% 
  summarise(centroid.x = mean(range(x)), 
            centroid.y = mean(range(y)),
            label = unique(State),
            `Apo` = unique(Apo),
            `Qt` = unique(Qt))

## drawing the plot
ggplot() + 
  geom_polygon(data = us_map1, 
               aes(x,y, group = group, fill = Qt), 
               color = "black",
               size = .1) +
  geom_label_repel(data = us_centroids1, 
                   aes(centroid.x, centroid.y, 
                       label = paste(region, "\n Apo (km/h) = ", `Apo`,  "\n Qt (m/s) =", `Qt`)),
                   size = 5/14*8,
                   box.padding = 1,
                   parse = F) +
  scale_fill_gradientn(name = expression(Q[t]~(m/s)),
                       breaks = c(0, seq(10,130,20)),
                       labels = c("", seq(10,130,20)),
                       limits = c(0, 130),
                       colors = c("#DCDCDC", "lightblue", "green"),
                       guide = guide_colorbar(barwidth = 0.8, barheight = 18)) +
  
  theme_void()

Answer 1

这有点痛苦，因为 plotmath 似乎没有换行符。因此，您必须使用atop() 来解决它。使用bquote() 将变量值插入到表达式中。这一次只对一个元素有效，因此我们必须对三个变量使用pmap()。

ggplot() + 
  geom_polygon(data = us_map1, 
               aes(x,y, group = group, fill = Qt), 
               color = "black",
               size = .1) +
  geom_label_repel(data = us_centroids1, 
                   aes(centroid.x, centroid.y, 
                       label = pmap(list(region, Apo, Qt), 
                                    \(x,y,z) bquote(atop(.(x), # first line of lab
                                                         atop(A[po] (km/h) == .(y), # second line
                                                              Q[t] (m/s) == .(z)) # third line
                                                         )
                                                    )
                                    )
                       ),
                   size = 5/14*8,
                   box.padding = 1,
                   parse = T) +
  scale_fill_gradientn(name = expression(Q[t]~(m/s)),
                       breaks = c(0, seq(10,130,20)),
                       labels = c("", seq(10,130,20)),
                       limits = c(0, 130),
                       colors = c("#DCDCDC", "lightblue", "green"),
                       guide = guide_colorbar(barwidth = 0.8, barheight = 18)) +
  theme_void()

^{由reprex package 创建于 2022-07-31 (v2.0.1)}