R: Format Markdown text

fmt_markdown {gt}

R Documentation

Format Markdown text

Description

Any Markdown-formatted text in the incoming cells will be transformed to the appropriate output type during render when using fmt_markdown().

Usage

fmt_markdown(
  data,
  columns = everything(),
  rows = everything(),
  md_engine = c("markdown", "commonmark")
)

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.
`columns`	Columns to target `⁠<column-targeting expression>⁠` // default: `everything()` Can either be a series of column names provided in `c()`, a vector of column indices, or a select helper function (e.g. `starts_with()`, `ends_with()`, `contains()`, `matches()`, `num_range()` and `everything()`).
`rows`	Rows to target `⁠<row-targeting expression>⁠` // default: `everything()` In conjunction with `columns`, we can specify which of their rows should undergo formatting. The default `everything()` results in all rows in `columns` being formatted. Alternatively, we can supply a vector of row captions within `c()`, a vector of row indices, or a select helper function (e.g. `starts_with()`, `ends_with()`, `contains()`, `matches()`, `num_range()`, and `everything()`). We can also use expressions to filter down to the rows we need (e.g., `⁠[colname_1] > 100 & [colname_2] < 50⁠`).
`md_engine`	Choice of Markdown engine `⁠singl-kw:[markdown\|commonmark]⁠` // default: `"markdown"` The engine preference for Markdown rendering. By default, this is set to `"markdown"` where gt will use the markdown package for Markdown conversion to HTML and LaTeX. The other option is `"commonmark"` and with that the commonmark package will be used.

Value

An object of class gt_tbl.

Targeting cells with `columns` and `rows`

Targeting of values is done through columns and additionally by rows (if nothing is provided for rows then entire columns are selected). The columns argument allows us to target a subset of cells contained in the resolved columns. We say resolved because aside from declaring column names in c() (with bare column names or names in quotes) we can use tidyselect-style expressions. This can be as basic as supplying a select helper like starts_with(), or, providing a more complex incantation like

where(~ is.numeric(.x) && max(.x, na.rm = TRUE) > 1E6)

which targets numeric columns that have a maximum value greater than 1,000,000 (excluding any NAs from consideration).

By default all columns and rows are selected (with the everything() defaults). Cell values that are incompatible with a given formatting function will be skipped over, like character values and numeric ⁠fmt_*()⁠ functions. So it's safe to select all columns with a particular formatting function (only those values that can be formatted will be formatted), but, you may not want that. One strategy is to format the bulk of cell values with one formatting function and then constrain the columns for later passes with other types of formatting (the last formatting done to a cell is what you get in the final output).

Once the columns are targeted, we may also target the rows within those columns. This can be done in a variety of ways. If a stub is present, then we potentially have row identifiers. Those can be used much like column names in the columns-targeting scenario. We can use simpler tidyselect-style expressions (the select helpers should work well here) and we can use quoted row identifiers in c(). It's also possible to use row indices (e.g., c(3, 5, 6)) though these index values must correspond to the row numbers of the input data (the indices won't necessarily match those of rearranged rows if row groups are present). One more type of expression is possible, an expression that takes column values (can involve any of the available columns in the table) and returns a logical vector. This is nice if you want to base formatting on values in the column or another column, or, you'd like to use a more complex predicate expression.

Compatibility of arguments with the `from_column()` helper function

from_column() can be used with the md_engine argument of fmt_markdown() to obtain varying parameter values from a specified column within the table. This means that each row could be formatted a little bit differently.

Please note that for this argument (md_engine), a from_column() call needs to reference a column that has data of the character type. Additional columns for parameter values can be generated with cols_add() (if not already present). Columns that contain parameter data can also be hidden from final display with cols_hide().

Examples

Create a few Markdown-based text snippets.

text_1a <- "
### This is Markdown.

Markdown's syntax is comprised entirely of
punctuation characters, which punctuation
characters have been carefully chosen so as
to look like what they mean... assuming
you've ever used email.
"

text_1b <- "
Info on Markdown syntax can be found
[here](https://daringfireball.net/projects/markdown/).
"

text_2a <- "
The **gt** package has these datasets:

 - `countrypops`
 - `sza`
 - `gtcars`
 - `sp500`
 - `pizzaplace`
 - `exibble`
"

text_2b <- "
There's a quick reference [here](https://commonmark.org/help/).
"

Arrange the text snippets as a tibble using dplyr::tribble(), then, create a gt table and format all columns with fmt_markdown().

dplyr::tribble(
  ~Markdown, ~md,
  text_1a,   text_2a,
  text_1b,   text_2b,
) |>
  gt() |>
  fmt_markdown(columns = everything()) |>
  tab_options(table.width = px(400))

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

fmt_markdown() can also handle LaTeX math formulas enclosed in "$..$" (inline math) and also "$$..$$" (display math). The following table has body cells that contain mathematical formulas in display mode (i.e., the formulas are surrounded by "$$"). Further to this, math can be used within md() wherever there is the possibility to insert text into the table (e.g., with cols_label(), tab_header(), etc.).

dplyr::tibble(
  idx = 1:5,
  l_time_domain =
    c(
      "$$1$$",
      "$${{\\bf{e}}^{a\\,t}}$$",
      "$${t^n},\\,\\,\\,\\,\\,n = 1,2,3, \\ldots$$",
      "$${t^p}, p > -1$$",
      "$$\\sqrt t$$"
    ),
  l_laplace_s_domain =
    c(
      "$$\\frac{1}{s}$$",
      "$$\\frac{1}{{s - a}}$$",
      "$$\\frac{{n!}}{{{s^{n + 1}}}}$$",
      "$$\\frac{{\\Gamma \\left( {p + 1} \\right)}}{{{s^{p + 1}}}}$$",
      "$$\\frac{{\\sqrt \\pi }}{{2{s^{\\frac{3}{2}}}}}$$"
    )
) |>
  gt(rowname_col = "idx") |>
  fmt_markdown() |>
  cols_label(
    l_time_domain = md(
      "Time Domain<br/>$\\small{f\\left( t \\right) =
      {\\mathcal{L}^{\\,\\, - 1}}\\left\\{ {F\\left( s \\right)} \\right\\}}$"
    ),
    l_laplace_s_domain = md(
      "$s$ Domain<br/>$\\small{F\\left( s \\right) =
      \\mathcal{L}\\left\\{ {f\\left( t \\right)} \\right\\}}$"
    )
  ) |>
  tab_header(
    title = md(
      "A (Small) Table of Laplace Transforms &mdash; $\\small{{\\mathcal{L}}}$"
    ),
    subtitle = md(
      "Five commonly used Laplace transforms and formulas.<br/><br/>"
    )
  ) |>
  cols_align(align = "center") |>
  opt_align_table_header(align = "left") |>
  cols_width(
    idx ~ px(50),
    l_time_domain ~ px(300),
    l_laplace_s_domain ~ px(600)
  ) |>
  opt_stylize(
    style = 2,
    color = "gray",
    add_row_striping = FALSE
  ) |>
  opt_table_outline(style = "invisible") |>
  tab_style(
    style = cell_fill(color = "gray95"),
    locations = cells_body(columns = l_time_domain)
  ) |>
  tab_options(
    heading.title.font.size = px(32),
    heading.subtitle.font.size = px(18),
    heading.padding = px(0),
    footnotes.multiline = FALSE,
    column_labels.border.lr.style = "solid",
    column_labels.border.lr.width = px(1)
  )

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

Function ID

3-27

Function Introduced

v0.2.0.5 (March 31, 2020)