Read merged cell tables headers to data frame

[JanMarvin]

This SO asked how to do this and the answer is surprisingly simple with openxlsx2:

openxlsx2::read_xlsx("filename.xlsx", fill_merged_cells = TRUE, start_row = 4, na.strings = "*")

The entire example looks like this:

library(openxlsx2)

### recreate example data
tmp <- temp_xlsx()
head <- data.frame(
  B = c("Single Detached Homes by Community, 2016, 2017, 2018", "Community", ""),
  C = c("", "Single Detached Homes", "2016"),
  D = c("", "", "2017"),
  E = c("", "", "2018")
)
head_dims <- wb_dims(x = head, from_col = "B", from_row = 2, col_names = FALSE)

data <- data.frame(
  B = c("100 Mile House", "Abbotsford", "Alert Bay", "Anmore"),
  C = c(25, 336, NA, 18),
  D = c(16, 252, NA, 18),
  E = c(19, 270, NA, 6)
)
data_dims <- wb_dims(x = data, from_col = "B", from_row = 2 + nrow(head), col_names = FALSE)

wb <- wb_workbook()$
  add_worksheet()$
  add_data(dims = head_dims,
            x = head, col_names = FALSE)$
  add_data(dims = data_dims,
            x = data, col_names = FALSE, na.strings = "*")$
  merge_cells(dims = "B2:E2")$
  merge_cells(dims = "B3:B4")$
  merge_cells(dims = "C3:E3")$
  set_col_widths(cols = "B:E", width = c(15, 10, 10, 10))$
  add_border(dims = head_dims, left_border = "medium", right_border = "medium", top_border = "medium", bottom_border = "medium", inner_hgrid = "medium", inner_vgrid = "medium")$
  add_border(dims = data_dims, left_border = "medium", right_border = "medium", top_border = "medium", bottom_border = "medium", inner_hgrid = "thin", inner_vgrid = "thin")$
  add_fill(dims = "B2:E2", color = wb_color("lightblue"))$
  add_cell_style(dims = "B3:E4", horizontal = "center")$
  add_cell_style(dims = "C5:E8", horizontal = "right")$
  add_ignore_error(dims = "C4:E4", number_stored_as_text = TRUE)$ # needs a fix from 1.3 devel
  save(tmp)

# cleanup
rm(wb, data, head, data_dims, head_dims)

###

# read a single data frame
wb_to_df(tmp, fill_merged_cells = TRUE, start_row = 4, na.strings = "*")
#>        Community 2016 2017 2018
#> 5 100 Mile House   25   16   19
#> 6     Abbotsford  336  252  270
#> 7      Alert Bay   NA   NA   NA
#> 8         Anmore   18   18    6

# same (read_xlsx is just a wrapper for wb_to_df())
read_xlsx(tmp, fill_merged_cells = TRUE, start_row = 4, na.strings = "*")
#>        Community 2016 2017 2018
#> 5 100 Mile House   25   16   19
#> 6     Abbotsford  336  252  270
#> 7      Alert Bay   NA   NA   NA
#> 8         Anmore   18   18    6