I am trying to have subscripts in my geom_label. e.g.

Maine
A_po (km/h) = 9
Q_t (m/s) = 90

I am aware of using [x] to get subscripts but I am not sure how to achieve that when I want to get the label values (partly) from a column. I tried using tidyeval (!!) to no avail. Even simply changing parse = T gives me errors. It could be something rudimentary that I am overlooking, but after reading this thread using plotmath in ggrepel labels, I am not sure if it is as simple as I thought.

Here is with what I have so far. I provided the packages and the data I have used, along with data cleaning/preparation steps. Finally, I've shown the code that I have used for creating the "preliminary" plot.

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()

CodePudding user response：

This is kind of a pain, since plotmath doesn't appear to have line breaks. Thus, you have to work around it with atop(). Use bquote() to insert variable values into the expression. This only works on one element at once, thus we have to pmap() over the three variables.

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()

^{Created on 2022-07-31 by the reprex package (v2.0.1)}