Great Tables Skill

great-tables is the Python implementation of the grammar of tables — the same grammar as R's gt, by the same author (Rich Iannone, Posit). It builds publication-quality display tables declaratively by layering formatting, structure, and style onto a GT() object. Use when execution language is Python and the task involves creating formatted data tables, cross-tabulations, or descriptive-statistics tables for reports and papers. great-tables accepts Polars DataFrames natively (DAAF's default) as well as pandas. For figures use plotnine (static) or plotly (interactive); for regression/model comparison tables great-tables has no modelsummary-style helper, so use the estimator's own tabular output instead (pyfixest etable(), statsmodels .summary()). R counterpart: the gt skill — substitute it when execution language is R.

What is great-tables?

great-tables implements a grammar of tables, analogous to plotnine/ggplot2's grammar of graphics but for tabular output:

• Declarative: build tables by chaining formatting, structure, and style methods
• Method-chaining: every method returns a new GT object, so operations chain with . (Python) rather than R's |> pipe
• Rich formatting: fmt_number, fmt_percent, fmt_currency, fmt_date, fmt_markdown, conditional styling, color scales
• Structured: header (title/subtitle), column spanners, row-group stub, grand summary rows, source notes, footnotes
• DataFrame-native: pass a Polars DataFrame directly to GT() (pandas also accepted; Polars is the DAAF default)

Probe-verified against installed 0.21.0 (2026-07-13): all API claims in this skill and its references were executed against the package. Version-specific caveats (e.g., grand_summary_rows expecting Polars expressions, cols_merge 0-based indices, save() needing selenium) are documented at their point of use.

Version Notes (0.21.0)

• Canonical constructor is gt.GT(df). The GT.from_data() classmethod is broken in 0.21.0 (raises TypeError on an internal _tbl_data kwarg) — do not use it. Probe: 04_extras_a.py in the R_Support sessionF scratch.
• grand_summary_rows(fns=...) expects Polars expressions, not R-style string aggregator names. Use {"Total": pl.all().sum()}, not {"Total": "sum"}. It also does not support the columns= selection argument in 0.21.0 (raises NotImplementedError) — summaries apply across all numeric columns.
• cols_merge(pattern=...) uses 0-based {0}, {1} indices — differs from R gt's 1-based {1}, {2}.
• HTML and LaTeX export work in-process (as_raw_html, write_raw_html, as_latex) — no external dependency.
• Image export (save() to PNG/PDF) does NOT work in the DAAF container — it requires selenium + a headless Chrome driver, neither of which is installed (and runtime pip install is blocked by DAAF policy). Export tables as HTML instead. See ./references/export.md.

How to Use This Skill

Reference File Structure

File	Purpose	When to Read
quickstart.md	GT() from a Polars DataFrame, header/source notes, basic fmt_* formatting	Starting out or need a quick table
formatting-structure.md	Full fmt_* family, tab_style/data_color styling, spanners, row-group stub, grand summary rows, cols_* operations	Detailed formatting and structure
export.md	as_raw_html/write_raw_html/as_latex, the save() image limitation, saving into project outputs	Saving or embedding tables

Reading Order

1. Quick data table? Start with quickstart.md
2. Complex formatting or structure? Read formatting-structure.md
3. Saving or embedding a table? Read export.md

Related Skills

Skill	Relationship
gt	R counterpart — same grammar of tables. Use gt when execution language is R; use great-tables when Python
polars	DAAF's default DataFrame library — great-tables accepts Polars DataFrames directly; build/aggregate the data in Polars, then format with great-tables
plotnine	Static figures (charts/plots) — use plotnine for figures, great-tables for tables
plotly	Interactive figures — use plotly for interactive charts, great-tables for tables
pyfixest	Regression output — great-tables has no modelsummary equivalent; use pyfixest etable() for FE/DiD model tables
statsmodels	Regression output — use statsmodels .summary() / summary2() for model tables
data-scientist	Methodology guidance for what to present in tables

R counterpart: For R pipelines, use the gt skill instead. great-tables and gt share the grammar of tables but differ in surface details (method chaining vs |>, 0-based vs 1-based cols_merge indices, Polars-expression vs string aggregators in summary rows, and export capabilities — see Version Notes).

Quick Decision Trees

"I need to make a table"

What kind of table?
├─ Data summary table (descriptive stats, crosstabs)
│   ├─ Simple (few rows/columns, minimal formatting)
│   │   └─ GT() + fmt_* → ./references/quickstart.md
│   └─ Complex (conditional styling, row groups, summary rows, color scales)
│       └─ tab_style / data_color / grand_summary_rows → ./references/formatting-structure.md
├─ Frequency / cross-tabulation table
│   └─ GT() with groupname_col row-group stub → ./references/formatting-structure.md
├─ Regression / model-coefficient table
│   └─ great-tables has NO modelsummary equivalent. Use the estimator's own output:
│       pyfixest etable() (FE/DiD) or statsmodels .summary() — see those skills
└─ Table with color scales or conditional formatting
    └─ data_color() or tab_style() → ./references/formatting-structure.md

"How do I save or embed it?"

Output target?
├─ HTML string (embed in a report, session workspace) → as_raw_html() → ./references/export.md
├─ HTML file on disk → write_raw_html() → ./references/export.md
├─ LaTeX (journal submission) → as_latex() → ./references/export.md
└─ PNG/PDF image → NOT available in the container (needs selenium/headless Chrome).
    Export HTML instead → ./references/export.md

File-First Execution in Research Workflows

In DAAF research pipelines, tables are generated through script files in scripts/stage8_analysis/, not interactively. This ensures auditability and reproducibility.

The pattern:

1. Write table code to scripts/stage8_analysis/{step}_{table-name}.py
2. Execute via bash {BASE_DIR}/scripts/run_with_capture.sh {script_path}
3. Output gets appended to the script as comments
4. Use write_raw_html() (or as_raw_html() + write) to save tables into the project output directory as HTML

See agent_reference/SCRIPT_EXECUTION_REFERENCE.md for the mandatory file-first execution protocol.

Quick Reference

Essential Setup

import polars as pl
import great_tables as gt
from great_tables import loc, style, md

Basic GT Table (from a Polars DataFrame)

tbl = (
    gt.GT(df, rowname_col="region", groupname_col="group")
    .tab_header(title="Revenue by Region", subtitle="FY2025")
    .tab_source_note(source_note=md("Source: *synthetic data*"))
    .fmt_currency(columns="revenue", currency="USD", decimals=2)
    .fmt_percent(columns="share", decimals=1)
    .cols_label(revenue="Revenue", share="Share")
)
html = tbl.as_raw_html()

Core GT Operations

Operation	Code
Create table (Polars or pandas)	gt.GT(df)
Row-group stub	gt.GT(df, rowname_col="id", groupname_col="grp")
Title/subtitle	.tab_header(title=..., subtitle=...)
Source note	.tab_source_note(source_note=md("Source: ..."))
Stubhead label	.tab_stubhead(label="...")
Format numbers	.fmt_number(columns=..., decimals=2)
Format percent	.fmt_percent(columns=..., decimals=1)
Format currency	.fmt_currency(columns=..., currency="USD")
Format date	.fmt_date(columns=..., date_style=...)
Markdown in cells	.fmt_markdown(columns=...)
Column spanner	.tab_spanner(label="...", columns=[...])
Grand summary rows	.grand_summary_rows(fns={"Total": pl.all().sum()})
Missing-value text	.sub_missing(missing_text="--")
Conditional style	.tab_style(style=style.fill(color="..."), locations=loc.body(...))
Color scale	.data_color(columns=[...], palette=["white", "blue"])
Column labels	.cols_label(col="Label")
Column align	.cols_align(align="right", columns=[...])
Hide columns	.cols_hide(columns=[...])
Merge columns	.cols_merge(columns=["lo","hi"], pattern="{0}–{1}")
Column width	.cols_width({"col": "150px"})
Export HTML string	.as_raw_html()
Write HTML file	.write_raw_html("table.html")
Export LaTeX	.as_latex()

Format Scalar Values (no table)

from great_tables import vals
vals.fmt_number([1234.5, 6789.0], decimals=1)   # ['1,234.5', '6,789.0']

Topic Index

Topic	Reference File
GT() from Polars/pandas	./references/quickstart.md
tab_header, tab_source_note, tab_stubhead	./references/quickstart.md
Basic fmt_number / fmt_percent / fmt_currency	./references/quickstart.md
cols_label column renaming	./references/quickstart.md
Full fmt_* family (date, markdown, integer, scientific, bytes)	./references/formatting-structure.md
Conditional styling (tab_style, loc, style)	./references/formatting-structure.md
Color scales (data_color)	./references/formatting-structure.md
Column spanners (tab_spanner)	./references/formatting-structure.md
Row-group stub (groupname_col, row_group_order)	./references/formatting-structure.md
Grand summary rows (Polars expressions)	./references/formatting-structure.md
sub_missing / sub_zero	./references/formatting-structure.md
Column operations (align, hide, move, merge, width)	./references/formatting-structure.md
Table options (opt_*, tab_options)	./references/formatting-structure.md
as_raw_html / write_raw_html	./references/export.md
as_latex	./references/export.md
save() image limitation (selenium)	./references/export.md
Saving into project outputs	./references/export.md

Citation

When great-tables is used as a primary table-formatting tool, include in the report's Software & Tools references:

Iannone, R., & Chow, M. (2024). great-tables: Easily generate information-rich, publication-quality tables from Python. Python package version 0.21.0. https://posit-dev.github.io/great-tables/

Cite when: great-tables produces tables included in the report or deliverables. Do not cite when: only used for quick exploratory tables not included in deliverables.