LT

Lightweight tables for R, inspired by gt.

lt provides a small grammar of tables that covers the structure most reports need — titles, column spanners, row groups, footnotes, and number formatting — without the heavy dependency stack. It targets HTML only (no LaTeX or RTF), which keeps the implementation minimal: the entire runtime is a single vanilla-JS file (about 10 KB minified).

Installation

# CRAN version
install.packages("lt")

# development version
install.packages("lt", repos = "https://yihui.r-universe.dev")

You may also play with the package at https://pkg.yihui.org/lt/playground/ without installing it.

Functions

lt() creates a table object from a data frame. The lt_*() functions build on it via the pipe. See https://pkg.yihui.org/lt/examples/01-lt#sec:cheatsheet for a "cheat table" as an overview of these functions.

Structure

• lt_header() — title and optional subtitle above the table.
• lt_spanner() — column-spanner label spanning a group of columns; or auto-infer spanners from column name prefixes.
• lt_group() — partition rows into labeled groups (rowspan or full-width separator style), either by column values or manual row indices.

Content & labels

• lt_label() — override column header labels.
• lt_footnote() — attach a numbered footnote to any region (title, subtitle, column, spanner, group, or body cells).
• lt_note() — append a plain unnumbered note below the table.
• lt_html() — render selected columns' cells as raw HTML instead of escaping them. For raw HTML in text (title, labels, footnotes, ...), wrap the text in I() in the corresponding function.

Formatting

• lt_format() — numeric formatting: decimal places, thousand separators, prefix/suffix, percentage, scientific notation, etc.
• lt_date() — date/datetime formatting using the browser locale.
• lt_sub() — substitute specific values (e.g., replace 0 with "—" or NA with "n/a").
• lt_merge() — merge several columns into one using a sprintf-style pattern.
• lt_indent() — indent selected rows (useful for hierarchical row labels).

Appearance

• lt_align() — set column alignment (left / center / right).
• lt_width() — set column widths.
• lt_style() — apply CSS classes or inline styles to cells, conditionally or unconditionally.
• lt_css() — attach an external CSS file or URL to the table.

Column order

• lt_move() — reorder columns.

Export

• lt_export() — save a table to a file: .html (optionally baking a static <table> that needs no JavaScript to view), .pdf, or .png (rendered via a headless Chromium browser).

Shiny

• lt_output() / render_lt() — Shiny UI and server bindings.

Examples

The R code below builds a table spec. Under the hood lt serializes it to a compact JSON object and ships it to the browser, where a tiny vanilla-JS runtime renders the <table>.

library(lt)

d = data.frame(
  Group = c("Treatment", "Treatment", "Control", "Control"),
  Endpoint = c("Primary", "Secondary", "Primary", "Secondary"),
  Estimate = c(0.6123, 0.7891, 0.4567, 0.5432),
  CI_Lower = c(0.4012, 0.5678, 0.2345, 0.3210),
  CI_Upper = c(0.8234, 1.0104, 0.6789, 0.7654),
  P_Value = c(0.0012, NA, 0.1234, NA)
)
lt(d) |>
  lt_group(~ Group) |>
  lt_header("Study Results", "Primary and secondary endpoints") |>
  lt_spanner(`95% CI` ~ CI_Lower + CI_Upper) |>
  lt_format(~ Estimate + CI_Lower + CI_Upper, decimals = 3) |>
  lt_sub(~ P_Value, missing = "—") |>
  lt_footnote("Two-sided p-value from log-rank test.", "column", ~ P_Value)

The same table can be built directly in JavaScript. Load lt.js once on the page, then call LT.build() from an inline <script> with the JSON spec:

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@xiee/utils/css/lt.min.css">
<script src="https://cdn.jsdelivr.net/npm/@xiee/utils/js/lt.min.js"></script>

<script>
LT.build({
  "data": {
    "Group":    ["Treatment", "Treatment", "Control", "Control"],
    "Endpoint": ["Primary", "Secondary", "Primary", "Secondary"],
    "Estimate": [0.6123, 0.7891, 0.4567, 0.5432],
    "CI_Lower": [0.4012, 0.5678, 0.2345, 0.3210],
    "CI_Upper": [0.8234, 1.0104, 0.6789, 0.7654],
    "P_Value":  [0.0012, null, 0.1234, null]
  },
  "ops": [
    { "type": "fmt_number", "columns": ["Estimate", "CI_Lower", "CI_Upper"], "decimals": 3 },
    { "type": "sub", "columns": ["P_Value"], "missing": "—" }
  ],
  "row_group": ["Group"],
  "header": { "title": "Study Results", "subtitle": "Primary and secondary endpoints" },
  "spanners": [{ "label": "95% CI", "columns": ["CI_Lower", "CI_Upper"] }],
  "footnotes": [{
    "text": "Two-sided p-value from log-rank test.",
    "location": { "type": "column_labels", "columns": ["P_Value"] }
  }]
});
</script>

LT.build() renders the table in place of the calling <script> tag. One lt.js inclusion handles any number of tables on the page.

You can find more examples at https://pkg.yihui.org/lt/examples.html.

Acknowledgements

This package was written with the help of Claude Code. lt is directly inspired by gt by Rich Iannone and the RStudio/Posit team. The grammar of tables that gt pioneered — layering titles, spanners, footnotes, and formatters onto a data frame — is a great idea; lt aims to provide a minimal re-implementation for contexts where a lighter footprint is preferred.