Chapter 3 Formatting and Rendering Tables

Table generation usually is a two step process

  1. Derive the cell value and tabulate them.
  2. Create the final table output, save it to a file to be shared with collaborators.

Chapter Commonly Used Tables focuses on the work involved in step 1. In this chapter we discuss the various aspects of creating the final output that is commonly stored in a file with a particular file format (pdf, txt, html, docx or rtf).

3.1 Title & Footnotes

Commonly rendered tables that are reported to the health authorities have titles and footnotes with information such as:

  • what is summarized in the table
  • database lock date
  • patient sub-population
  • notes by study team
  • notes regarding statistical algorithms chosen
  • provenance information including path to program and when the table was created

Often footnotes include cell references.

3.1.1 gt

The gt package lets you add a title and even a subtitle and preheader lines (for RTF) with its tab_header() function. In the following example, we create some sample_data and feed that into the gt() function. We can automatically create a table stub (for row labels) and row groups with the rowname_col and groupname_col arguments of gt().

Code
resetSession()
library(gt)

sample_data <-
  dplyr::tibble(
    label = c("n", "Mean (SD)", "Median", "Min - Max", "F", "M", "U", "UNDIFFERENTIATED"),
    `val_A: Drug X` = c(134, 33.8, 33, NA, 79, 51, 3, 1),
    `val_B: Placebo` = c(134, 35.4, 35, NA, 77, 55, 2, 0),
    `val_C: Combination` = c(132, 35.4, 35, NA, 66, 60, 4, 2),
    category = c(rep("Age (Years)", 4), rep("Sex, n (%)", 4))
  )

gt_tbl <-
  gt(
    sample_data, 
    rowname_col = "label",
    groupname_col = "category"
  ) |>
  tab_header(
    title = "x.x: Study Subject Data",
    subtitle = md(
      "x.x.x: Demographic Characteristics  \n Table x.x.x.x: Demographic
      Characteristics - Full Analysis Set"
    ),
    preheader = c("Protocol: XXXXX", "Cutoff date: DDMMYYYY")
  ) |> 
  tab_source_note("Source: ADSL DDMMYYYY hh:mm; Listing x.xx; SDTM package: DDMMYYYY") |> 
  sub_missing(missing_text = "") |> 
  tab_options(
    page.orientation = "landscape",
    page.numbering = TRUE,
    page.header.use_tbl_headings = TRUE,
    page.footer.use_tbl_notes = TRUE
  )

gt_tbl
x.x: Study Subject Data
x.x.x: Demographic Characteristics
Table x.x.x.x: Demographic Characteristics - Full Analysis Set
val_A: Drug X val_B: Placebo val_C: Combination
Age (Years)
n 134.0 134.0 132.0
Mean (SD) 33.8 35.4 35.4
Median 33.0 35.0 35.0
Min - Max


Sex, n (%)
F 79.0 77.0 66.0
M 51.0 55.0 60.0
U 3.0 2.0 4.0
UNDIFFERENTIATED 1.0 0.0 2.0
Source: ADSL DDMMYYYY hh:mm; Listing x.xx; SDTM package: DDMMYYYY

The above example contains the use of the tab_source_note() function. You can create as many source notes in the table footer as you need, and they typically describe the data table as a whole (i.e., not pointing to anything specific). For that, you can use footnotes and target cells that require additional explanation. Here’s an example of that using tab_footnote():

Code
gt_tbl |>
  tab_footnote(
    footnote = "This is the combination of the two.",
    locations = cells_column_labels(columns = `val_C: Combination`)
  ) |>
  tab_footnote(
    footnote = "These values are the same.",
    locations = cells_body(
      columns = matches("_A|_B"), rows = "n"
      )
  )
x.x: Study Subject Data
x.x.x: Demographic Characteristics
Table x.x.x.x: Demographic Characteristics - Full Analysis Set
val_A: Drug X val_B: Placebo val_C: Combination1
Age (Years)
n 2 134.0 2 134.0 132.0
Mean (SD) 33.8 35.4 35.4
Median 33.0 35.0 35.0
Min - Max


Sex, n (%)
F 79.0 77.0 66.0
M 51.0 55.0 60.0
U 3.0 2.0 4.0
UNDIFFERENTIATED 1.0 0.0 2.0
Source: ADSL DDMMYYYY hh:mm; Listing x.xx; SDTM package: DDMMYYYY
1 This is the combination of the two.
2 These values are the same.

The tab_footnote() function allows for footnotes to be placed anywhere in the table (using the cells_*() helper functions for targeting). Targeting columns, rows, or other locations can be done with Tidyselect-style helper functions (e.g., matches(), starts_with(), etc.), ID values, or indices.

As a final note on the first example, we can specify certain page.* options that make RTF output ideal for regulatory filing purposes. The options employed above in the tab_options() call ensure that pages are in landscape orientation, page numbering for each table is activated, and that page header and footer are used for the table’s headings and footer elements.

3.1.2 rtables

The basic_table() function in rtables has the arguments titles, subtitles, main_footer, prov_footer to add titles and footnotes to tables. rtables also supports referential footnotes.

So for example a basic demographics table created with rtables via tern with title and footnotes would look as follows:

Code
resetSession()
library(rtables)

lyt <- basic_table(
  title = "Demographic Table - All Patients",
  subtitles = c("Cutoff Date: June 01, 2022", "Arm B received a placebo."),
  main_footer = c("Missing data is omitted.")
) |>
  split_cols_by("ARM") |>
  analyze(c("AGE", "SEX"))

build_table(lyt, adsl)
Demographic Table - All Patients
Cutoff Date: June 01, 2022
Arm B received a placebo.

————————————————————————————————————————————————
         A: Drug X   B: Placebo   C: Combination
————————————————————————————————————————————————
AGE                                             
  Mean     33.77       35.43          35.43     
SEX                                             
  F         79           82             70      
  M         55           52             62      
————————————————————————————————————————————————

Missing data is omitted.

3.1.3 flextable

Titles and notes can be added and formatted with the flextable package. It is possible to add them in the header and in the footer. Several methods are possible but for most needs, the add_header_lines() and add_footer_lines() functions will be the easiest to use.

Let’s create first a flextable from an aggregation that will be used to illustrate the features.

Code
resetSession()
library(flextable)
library(dplyr)

z <- adsl |> 
  group_by(ARM, SEX) |>
  summarise(avg = mean(AGE), sd = sd(AGE)) |>
  tabulator(rows = "SEX", columns = "ARM",
    Y = as_paragraph(avg, " (", sd, ")")) |> 
  as_flextable()
z

SEX

A: Drug X

B: Placebo

C: Combination

F

32.8 (6.1)

34.2 (7.0)

35.2 (7.4)

M

35.2 (7.0)

37.3 (8.9)

35.7 (8.2)

The following shows how to add titles or notes:

Code
z |>
  add_header_lines("hello world") |>
  add_footer_lines("bye bye world")

hello world

SEX

A: Drug X

B: Placebo

C: Combination

F

32.8 (6.1)

34.2 (7.0)

35.2 (7.4)

M

35.2 (7.0)

37.3 (8.9)

35.7 (8.2)

bye bye world

For Word output, users can prepend a table number that will auto-incremente.

Code
docx_file <- "reports/flextable-title-01.docx"
ft <- add_header_lines(z, "hello world") |>
  prepend_chunks(
    i = 1, j = 1, part = "header", 
    as_chunk("Table "), as_word_field("SEQ tab \u005C* Arabic"), 
    as_chunk(": ")) |>
  add_footer_lines("bye bye world") |>
  theme_vanilla()
save_as_docx(ft, ft, path = docx_file)

Footnotes are also available in flextable with function footnote(). The function lets users add footnotes and references to it on the table.

Code
footnote(z, i = c(1, 2, 2), j = c(1, 5, 7), 
         value = as_paragraph("hello world"), ref_symbols = "(1)")

SEX

A: Drug X

B: Placebo

C: Combination

F(1)

32.8 (6.1)

34.2 (7.0)

35.2 (7.4)

M

35.2 (7.0)

37.3 (8.9)(1)

35.7 (8.2)(1)

(1)hello world

3.1.4 tfrmt

The tfrmt() function in the tfrmt package includes the arguments title and subtitle to add titles. Within the footnote_plan() function, the user can nest multiple footnote_structures to add footnotes with superscript reference symbols on groups, columns or labels.

To demonstrate, this example will create a mock demographics table:

Code
resetSession()
library(tfrmt)
library(dplyr)
library(tidyr)

# Create mock data
df <- crossing(group = c("AGE", "SEX"),
               label = c("label 1", "label 2"),
               column = c("Drug X", "Placebo", "Combination"),
               param = c("count", "percent"))

# Create specification
tfrmt_spec <- tfrmt(
  # Add titles
  title = "Demographic Table - All Patients",
  subtitle = "Cutoff Date: June 01, 2022. Arm B received a placebo.",

  # Specify table features
  group = group,
  label = label,
  column = column,
  param = param,
  row_grp_plan = row_grp_plan(
    row_grp_structure(group_val = ".default",
                      element_block(post_space = "   ")) ),

  # Define cell formatting
  body_plan = body_plan(
    frmt_structure(group_val = ".default", label_val = ".default",
                   frmt_combine("{count} ({percent})",
                                count = frmt("xx"),
                                percent = frmt("xx.x")))),

  # Add footnotes here
  footnote_plan = footnote_plan(
    footnote_structure(footnote_text = "Footnote about column", column_val = "Combination"),
    footnote_structure(footnote_text = "Footnote about group", group_val = "AGE"),
    marks = "numbers"),

)

print_mock_gt(tfrmt_spec, df)
Demographic Table - All Patients
Cutoff Date: June 01, 2022. Arm B received a placebo.
Combination1 Drug X Placebo
AGE2


  label 1 xx (xx.x) xx (xx.x) xx (xx.x)
  label 2 xx (xx.x) xx (xx.x) xx (xx.x)
         
SEX


  label 1 xx (xx.x) xx (xx.x) xx (xx.x)
  label 2 xx (xx.x) xx (xx.x) xx (xx.x)
         
1 Footnote about column
2 Footnote about group

See this vignette for more details on footnotes: link to website

3.1.5 tables

The tables package concentrates on the table itself. The titles are generally written as part of the surrounding document. Footnotes would be added after constructing the table by modifying individual entries.

Alternatively for HTML output, only the footnote markers need to be added by modifying entries, and then the footnotes can be applied by using toHTML(tab, options = list(doFooter = TRUE, HTMLfooter = HTMLfootnotes(...)).

Code
resetSession()
adsl <- cadsl

library(tables)
table_options(doCSS = TRUE)

sd_in_parens <- function(x) sprintf("(%.1f)", sd(x))

tab <- tabular(SEX ~ Heading()*ARM*
                     Heading()*AGE*
                     Heading()*(mean + sd_in_parens), 
               data = adsl)

rowLabels(tab)[1,1] <- paste(rowLabels(tab)[1,1], "<sup>a</sup>")
tab[2,2] <- sprintf("%s%s", tab[2,2], "<sup>b</sup>")
tab[2,3] <- sprintf("%.2f%s", tab[2,3], "<sup>b</sup>")

footnotes <- HTMLfootnotes(tab, a = "This is a label footnote.",
                                b = "These are cell footnotes.")
toHTML(tab, options = list(HTMLfooter = footnotes,
                           doFooter = TRUE))
SEX A: Drug X B: Placebo C: Combination
aThis is a label footnote.
bThese are cell footnotes.
F a 32.76 (6.1) 34.24 (7.0) 35.20 (7.4)
M 35.22 (7.0)b 37.31b (8.9) 35.69 (8.2)

3.1.6 tidytlg

The gentlg() function in the tidytlg package includes the title argument for adding title and the footers argument for adding footnotes to the table output. Users can include a vector of character strings for multiple lines of footnotes (please see an example below). At the bottom line of the footnotes, the file name of the table and the path of the table program along with the datetime stamp are automatically created.

Code
resetSession()
library(dplyr)
library(tidytlg)

adsl <- formatters::ex_adsl 

# create analysis set row
t1 <- freq(adsl,
           rowvar = "ITTFL",
           colvar = "ARM",
           statlist = statlist("n"),
           subset = ITTFL == "Y",
           rowtext = "Analysis set: ITT") 

# create univariate stats for age
t2 <- univar(adsl,
               rowvar = "AGE",
               colvar = "ARM",
               statlist = statlist(c("N", "MEANSD", "MEDIAN", "RANGE", "IQRANGE")),
               row_header = "Age (years)",
               decimal = 0)

tbl <- bind_table(t1, t2)

# assign table id
tblid <- "Table01"

# output the analysis results
gentlg(huxme       = tbl,
       format      = "HTML",
       print.hux = FALSE,
       file        = tblid,
       orientation = "portrait",
       title = "Demographic and Baseline Characteristics; Intent-to-treat Analysis Set",
       footers = c("Key: IQ = Interquartile","Note: N reflects non-missing values"),
       colheader = c("","A: Drug X","B: Placebo","C: Combination"))
Table01:   Demographic and Baseline Characteristics; Intent-to-treat Analysis Set
A: Drug X
B: Placebo
C: Combination
Analysis set: ITT
134134132
Age (years)
N
134134132
Mean (SD)
33.8 (6.55)35.4 (7.90)35.4 (7.72)
Median
33.035.035.0
Range
(21; 50)(21; 62)(20; 69)
IQ range
(28.0; 39.0)(30.0; 40.0)(30.0; 40.0)

Key: IQ = Interquartile
Note: N reflects non-missing values
[table01.html][/home/runner/work/_temp/1a2425bf-3fe6-411c-8f06-c8509a18b561] 06JUN2024, 16:29

To programmatically incorporate titles and footnotes into each table program, users can create an excel file called titles.xls (see below snapshot) with the columns of "TABLE ID","IDENTIFIER","TEXT". In the gentlg() function call, users just need to provide the argument of title_file for specifying the location of titles.xls. Then the title and footnotes corresponding to the table ID will be automatically included in the table output. Users need to make sure the correct table ID is used for the file argument of the gentlg() function call.

Code
gentlg(huxme       = tbl,
       format      = "HTML",
       print.hux = FALSE,
       file        = tblid,
       orientation = "portrait",
       title_file = system.file("extdata/titles.xls", package = "tidytlg"),
       colheader = c("","A: Drug X","B: Placebo","C: Combination"))

3.2 Captions

A caption is a single paragraph of text describing the table. Captions are often used because they allow you to cross-reference tables or list them in a ‘list of tables’ with the corresponding page numbers.

3.2.1 flextable

The set_caption() function in flextable is the recommended way to add captions.

Code
resetSession()
library(flextable)

flextable(head(cars)) |>
  set_caption(
    caption = "a caption",
    autonum = officer::run_autonum(seq_id = "tab", bkm = "flextable-label"))
``` ```{=html}
(\#tab:flextable-label)a caption

speed

dist

4

2

4

10

7

4

7

22

8

16

9

10

In bookdown, use the syntax \@ref(tab:flextable-label) to create a linked reference to the table. Here is an example of a reference: ??.

With Quarto, the R chunk code should be transformed as:

Code
#| label: tbl-flextable-label
#| tbl-cap: a caption
flextable(head(cars))

3.2.2 tables

As with titles, captions would be added as part of the surrounding document rather than part of the table object.

3.4 Rendering Tables

The choice of output format is often dictated by your company’s processes to include the tables in a report. The packages discussed in this book vary in regard to which output formats are supported natively. The following table shows the current output capabilities for each package.

ASCII PDF HTML .docx RTF .pptx grid
flextable
gt
rtables
tables
tfrmt
tidytlg

If the format you need is not supported by the package you would like to use, there are still options. For example, tables produced in rtables and tables can be converted to flextable objects, giving access to the other output formats. Pandoc (MacFarlane 2023) is another option: it can convert documents between a wide range of document formats.

References

MacFarlane, John. 2023. Pandoc. https://pandoc.org.