Change empty cells in gtsummary::tbl_merge

Question

I have merged two tables with different rows, resulting in empty cells. I would like to replace the empty cell with an explicit "Missing" or "---" (this may also be something to implement within tbl_merge for a future feature). I tried playing around with the superstar function modify_table_styling but am having trouble finding the rows. I've tried everything() and is.na(estimate). Also, note that I actually have a tbl_merge on a tbl_merge, so my my_df$table_body is even more complex to find row identifiers in.

Thank you for your help!

library(gtsummary)
library(dplyr)

tbl_dense <-
  trial %>%
  tbl_summary(by = trt)

tbl_sparse <-
  trial %>%
  select(trt, response) %>%
  tbl_summary(by = trt)

tbl_merge(list(tbl_dense, tbl_sparse)) %>% 
  as_kable()

Characteristic	Drug A, N = 98	Drug B, N = 102	Drug A, N = 98	Drug B, N = 102
Age	46 (37, 59)	48 (39, 56)
Unknown	7	4
Marker Level (ng/mL)	0.84 (0.24, 1.57)	0.52 (0.19, 1.20)
Unknown	6	4
T Stage
T1	28 (29%)	25 (25%)
T2	25 (26%)	29 (28%)
T3	22 (22%)	21 (21%)
T4	23 (23%)	27 (26%)
Grade
I	35 (36%)	33 (32%)
II	32 (33%)	36 (35%)
III	31 (32%)	33 (32%)
Tumor Response	28 (29%)	33 (34%)	28 (29%)	33 (34%)
Unknown	3	4	3	4
Patient Died	52 (53%)	60 (59%)
Months to Death/Censor	23.5 (17.4, 24.0)	21.2 (14.6, 24.0)

  
# Likely with this do-it-all function
# modify_table_styling(
#   column = estimate,
#   rows = is.na(estimate), # Not sure how to select rows
#   missing_symbol = "MISSING"
# )

^{Created on 2021-07-30 by the reprex package (v2.0.0)}

Answer 1

You're right, the modify_table_styling() function is the way to go. Example below!

library(gtsummary)
packageVersion("gtsummary")

tbl_dense <-
  trial %>%
  tbl_summary(by = trt)

tbl_sparse <-
  trial %>%
  select(trt, response) %>%
  tbl_summary(by = trt)

tbl <-
  tbl_merge(list(tbl_dense, tbl_sparse)) %>%
  modify_table_styling(
    columns = everything(),
    rows = !is.na(variable),
    missing_symbol = "MISSING"
  )