List total N in header of tbl_stack - r

Question

When I do a tbl_stack, I'd like to show the total N of the combined tables in the tbl_stack in the header. At the moment the result appears to show the N of the first table in the stack.
trial %>%
select(age, grade, response, trt) %>%
filter(grade == "I") %>%
tbl_summary(
by = trt,
label = list(age ~ "Patient Age"),
statistic = list(all_continuous() ~ "{mean} ({sd})"),
digits = list(age ~ c(0, 1))
)
tbl_summary_ex2a <-
trial %>%
select(age, grade, response, trt) %>%
filter(grade %in% c("II", "III", "IV")) %>%
tbl_summary(
by = trt,
label = list(age ~ "Patient Age"),
statistic = list(all_continuous() ~ "{mean} ({sd})"),
digits = list(age ~ c(0, 1))
)
tbl_stack(tbls=list(tbl_summary_ex2, tbl_summary_ex2a))
Thanks for any tips,
Jeff

Answer 1

Yes, as the documentation of tbl_stack() indicates, the headers are retained from the first gtsummary in the stack. You can use the modify_header() function to change the headers, however. Additionally, these gtsummary tables have an internal object, .$df_by, that saves the Ns from each of your tables. You can sum the Ns across tables using these internal data frames. Example below doing this programmatically, but if it's easier you could simply hard code the Ns.
library(gtsummary)
library(tidyverse)
tbl_summary_ex2 <-
trial %>%
select(age, grade, response, trt) %>%
filter(grade == "I") %>%
tbl_summary(
by = trt,
label = list(age ~ "Patient Age"),
statistic = list(all_continuous() ~ "{mean} ({sd})"),
digits = list(age ~ c(0, 1)),
include = -grade
)
tbl_summary_ex2a <-
trial %>%
select(age, grade, response, trt) %>%
filter(grade %in% c("II", "III", "IV")) %>%
tbl_summary(
by = trt,
label = list(age ~ "Patient Age"),
statistic = list(all_continuous() ~ "{mean} ({sd})"),
digits = list(age ~ c(0, 1)),
include = -grade
)
# calculate the sum total Ns from both tables
list_N <-
tbl_summary_ex2$df_by %>%
bind_rows(tbl_summary_ex2a$df_by) %>%
select(by_col, by, n) %>%
group_by(by_col, by) %>%
summarise(n = sum(n)) %>%
mutate(
header_update =
str_glue("{by_col} ~ '**{by}**, N = {n}'") %>%
as.formula() %>%
list()
) %>%
pull(header_update)
list_N
tbl_stack(
tbls=list(tbl_summary_ex2, tbl_summary_ex2a),
group_header = c("Grade I", "Grade > I")
) %>%
modify_header(list_N)