R: Add a table header

tab_header {gt}

R Documentation

Add a table header

Description

We can add a table header to the gt table with a title and even a subtitle using tab_header(). A table header is an optional table part that is positioned just above the column labels table part. We have the flexibility to use Markdown or HTML formatting for the header's title and subtitle with the md() and html() helper functions.

Usage

tab_header(data, title, subtitle = NULL, preheader = NULL)

Arguments

`data`	The gt table data object `⁠obj:<gt_tbl>⁠` // required This is the gt table object that is commonly created through use of the `gt()` function.
`title`	Header title `⁠scalar<character>⁠` // required Text to be used in the table title. We can elect to use the `md()` and `html()` helper functions to style the text as Markdown or to retain HTML elements in the text.
`subtitle`	Header subtitle `⁠scalar<character>⁠` // default: `NULL` (`optional`) Text to be used in the table subtitle. We can elect to use `md()` or `html()` helper functions to style the text as Markdown or to retain HTML elements in the text.
`preheader`	RTF preheader text `⁠vector<character>⁠` // default: `NULL` (`optional`) Optional preheader content that is rendered above the table for RTF output. Can be supplied as a vector of text.

Value

An object of class gt_tbl.

Examples

Let's use a small portion of the gtcars dataset to create a gt table. A header part can be added to the table with the tab_header() function. We'll add a title and the optional subtitle as well. With md(), we can make sure the Markdown formatting is interpreted and transformed.

gtcars |>
  dplyr::select(mfr, model, msrp) |>
  dplyr::slice(1:5) |>
  gt() |>
  tab_header(
    title = md("Data listing from **gtcars**"),
    subtitle = md("`gtcars` is an R dataset")
  )

This image of a table was generated from the first code example in the `tab_header()` help file.

If the table is intended solely as an HTML table, you could introduce your own HTML elements into the header. You can even use the htmltools package to help arrange and generate the HTML. Here's an example of that, where two ⁠<div>⁠ elements are placed in a htmltools::tagList().

gtcars |>
  dplyr::select(mfr, model, msrp) |>
  dplyr::slice(1:5) |>
  gt() |>
  tab_header(
    title =
      htmltools::tagList(
        htmltools::tags$div(
          htmltools::HTML(
            web_image("https://www.r-project.org/logo/Rlogo.png")
          ),
          style = htmltools::css(`text-align` = "center")
        ),
        htmltools::tags$div(
          "Data listing from ", htmltools::tags$strong("gtcars")
        )
      )
  )

This image of a table was generated from the second code example in the `tab_header()` help file.

If using HTML but doing something far simpler, we can wrap our title or subtitle inside html() to declare that the text provided is HTML.

gtcars |>
  dplyr::select(mfr, model, msrp) |>
  dplyr::slice(1:5) |>
  gt() |>
  tab_header(
    title = html("Data listing from <strong>gtcars</strong>"),
    subtitle = html("From <span style='color:red;'>gtcars</span>")
  )

This image of a table was generated from the third code example in the `tab_header()` help file.

Sometimes, aligning the heading elements to the left can improve the presentation of a table. Here, we use the nuclides dataset to generate a display of natural abundance values for several stable isotopes. opt_align_table_header() is used with align = "left" to make it so the title and subtitle are left aligned in the header area.

nuclides |>
  dplyr::filter(!is.na(abundance)) |>
  dplyr::filter(abundance != 1) |>
  dplyr::filter(z >= 1 & z <= 8) |>
  dplyr::mutate(element = paste0(element, ", **z = ", z, "**")) |>
  dplyr::mutate(nuclide = gsub("[0-9]+$", "", nuclide)) |>
  dplyr::select(nuclide, element, atomic_mass, abundance, abundance_uncert) |>
  gt(
    rowname_col = "nuclide",
    groupname_col = "element",
    process_md = TRUE
  ) |>
  tab_header(
    title = "Natural Abundance Values",
    subtitle = md("For elements having atomic numbers from `1` to `8`.")
  ) |>
  tab_stubhead(label = "Isotope") |>
  tab_stub_indent(
    rows = everything(),
    indent = 1
  ) |>
  fmt_chem(columns = stub()) |>
  fmt_number(
    columns = atomic_mass,
    decimals = 4,
    scale_by = 1 / 1e6
  ) |>
  fmt_percent(
    columns = contains("abundance"),
    decimals = 4
  ) |>
  cols_merge_uncert(
    col_val = abundance,
    col_uncert = abundance_uncert
  ) |>
  cols_label_with(fn = function(x) tools::toTitleCase(gsub("_", " ", x))) |>
  cols_width(
    stub() ~ px(70),
    atomic_mass ~ px(120),
    abundance ~ px(200)
  ) |>
  opt_align_table_header(align = "left") |>
  opt_vertical_padding(scale = 0.5)

This image of a table was generated from the fourth code example in the `tab_header()` help file.

Function ID

2-1

Function Introduced

v0.2.0.5 (March 31, 2020)