LaTeX Mastery: Automating Scientific Data Tables

JSON to LaTeX Table: booktabs, siunitx, multicolumn, longtable, and Special Character Escaping

Publication-quality LaTeX tables require more than wrapping rows in tabular — they use booktabs for professional horizontal rules, siunitx's S column type to align decimal points automatically, \multirow and \multicolumn for merged cells, longtable for data that spans multiple pages, and rigorous special-character escaping (underscores, ampersands, percent signs all have LaTeX meaning). This guide covers programmatic JSON-to-LaTeX generation that handles all of these correctly, plus a Node.js conversion pipeline for research workflows.

Live Example: Professional booktabs Table from JSON

// Input JSON: ML model benchmark results
const results = [
  { model: "GPT-4o",      task: "MMLU",      accuracy: 88.7, params_b: 1800, latency_ms: 340,  open_source: false },
  { model: "Llama 3 70B", task: "MMLU",      accuracy: 82.0, params_b: 70,   latency_ms: 95,   open_source: true  },
  { model: "Mistral 8x7B",task: "MMLU",      accuracy: 79.1, params_b: 46.7, latency_ms: 62,   open_source: true  },
  { model: "GPT-4o",      task: "HumanEval", accuracy: 90.2, params_b: 1800, latency_ms: 310,  open_source: false },
  { model: "Llama 3 70B", task: "HumanEval", accuracy: 81.1, params_b: 70,   latency_ms: 88,   open_source: true  },
];

// Special characters that must be escaped in LaTeX text mode:
const LATEX_ESCAPES: Record<string, string> = {
  '&': '\\&',   '%': '\\%',   '$': '\\$',   '#': '\\#',
  '_': '\\_',   '{': '\\{',   '}': '\\}',   '~': '\\textasciitilde{}',
  '^': '\\textasciicircum{}', '\\': '\\textbackslash{}',
};

function escapeLatex(str: string): string {
  return str.replace(/[&%$#_{}~^\\]/g, ch => LATEX_ESCAPES[ch] ?? ch);
}

function formatNumber(n: number, decimals = 1): string {
  return n.toFixed(decimals);
}

function jsonToLatexTable(data: typeof results): string {
  // Find max accuracy per task for bolding
  const maxByTask: Record<string, number> = {};
  data.forEach(r => {
    maxByTask[r.task] = Math.max(maxByTask[r.task] ?? 0, r.accuracy);
  });

  const rows = data.map(r => {
    const accStr = formatNumber(r.accuracy);
    const bold   = r.accuracy === maxByTask[r.task];
    const accCell = bold ? `\\textbf{${accStr}}` : accStr;

    return [
      escapeLatex(r.model),
      escapeLatex(r.task),
      accCell,
      formatNumber(r.params_b, 0),
      formatNumber(r.latency_ms, 0),
      r.open_source ? '$\\checkmark$' : '---',
    ].join(' & ') + ' \\\\';
  });

  return `\\begin{table}[htbp]
\\centering
\\caption{LLM Benchmark Comparison}
\\label{tab:llm-benchmarks}
\\begin{tabular}{llSSSc}
\\toprule
\\textbf{Model} & \\textbf{Task} & {\\textbf{Accuracy (\\%)}} & {\\textbf{Params (B)}} & {\\textbf{Latency (ms)}} & {\\textbf{Open Source}} \\\\
\\midrule
${rows.join('\n')}
\\bottomrule
\\end{tabular}
\\end{table}`;
}

// Output:
// \\begin{table}[htbp]
// \\centering
// \\caption{LLM Benchmark Comparison}
// \\label{tab:llm-benchmarks}
// \\begin{tabular}{llSSSc}
// \\toprule
// \\textbf{Model} & \\textbf{Task} & {\\textbf{Accuracy (\\%)}} ...
// \\midrule
// GPT-4o & MMLU & \\textbf{88.7} & 1800 & 340 & --- \\\\
// ...

siunitx S Column for Decimal Alignment

% siunitx S column aligns numbers at the decimal point automatically
% No manual padding needed — siunitx handles alignment mathematically

% Preamble: \\usepackage{siunitx}

\\begin{tabular}{l S[table-format=3.1] S[table-format=4.0] S[table-format=3.0]}
\\toprule
Model & {Accuracy (\\%)} & {Parameters (B)} & {Latency (ms)} \\\\
\\midrule
GPT-4o        & 88.7 & 1800 &  340 \\\\
Llama 3 70B   & 82.0 &   70 &   95 \\\\
Mistral 8x7B  & 79.1 &  46.7 &  62 \\\\
\\bottomrule
\\end{tabular}

% S column options:
% table-format=3.1   — up to 3 digits before, 1 after decimal point
% table-format=4.0   — up to 4 digits, no decimal
% round-mode=places, round-precision=2   — round to 2 decimal places
% table-number-alignment=center  — center the column

% In the Node.js generator, wrap numeric headers in {braces}:
// S columns require header text in {braces} to suppress numeric treatment
const numericCols = ['accuracy', 'params_b', 'latency_ms'];
const header = cols.map(c =>
  numericCols.includes(c.key) ? `{${escapeLatex(c.label)}}` : `\\textbf{${escapeLatex(c.label)}}`
).join(' & ');

multicolumn and multirow for Group Headers

% JSON with grouped columns:
const experiments = [
  { model: "GPT-4o",    train_acc: 92.1, train_loss: 0.21, test_acc: 88.7, test_loss: 0.31 },
  { model: "Llama 3",   train_acc: 85.3, train_loss: 0.38, test_acc: 82.0, test_loss: 0.44 },
];

% Generated LaTeX with group headers:
\\begin{tabular}{lSSss}
\\toprule
\\multirow{2}{*}{\\textbf{Model}} &
  \\multicolumn{2}{c}{\\textbf{Training}} &
  \\multicolumn{2}{c}{\\textbf{Test}} \\\\
\\cmidrule(lr){2-3} \\cmidrule(lr){4-5}
& {Acc (\\%)} & {Loss} & {Acc (\\%)} & {Loss} \\\\
\\midrule
GPT-4o  & 92.1 & 0.21 & 88.7 & 0.31 \\\\
Llama 3 & 85.3 & 0.38 & 82.0 & 0.44 \\\\
\\bottomrule
\\end{tabular}

% \\cmidrule(lr){2-3} — partial horizontal rule spanning columns 2–3
% (lr) adds small gaps on left and right to visually separate groups
% \\multirow{2}{*}{...} — span 2 rows, auto width

longtable for Multi-Page Tables

% For tables with 50+ rows that span multiple pages
% \\usepackage{longtable}

function jsonToLongtable(data: Record<string, unknown>[], cols: ColDef[]): string {
  const colSpec   = cols.map(c => c.align === 'number' ? 'S' : 'l').join('');
  const headerRow = cols.map(c => `{\\textbf{${escapeLatex(c.label)}}}`).join(' & ');
  const sepRow    = `\\midrule\n\\endhead`;

  const rows = data.map(r =>
    cols.map(c => {
      const v = r[c.key];
      if (typeof v === 'number') return formatNumber(v, c.decimals ?? 2);
      return escapeLatex(String(v ?? ''));
    }).join(' & ') + ' \\\\'
  ).join('\n');

  return `\\begin{longtable}{${colSpec}}
\\caption{${escapeLatex(caption)}} \\label{tab:${label}} \\\\
\\toprule
${headerRow} \\\\
\\midrule
\\endfirsthead
% Repeated header on subsequent pages
\\multicolumn{${cols.length}}{c}{\\tablename\\ \\thetable{} (continued)} \\\\
\\toprule
${headerRow} \\\\
${sepRow}
${rows}
\\bottomrule
\\end{longtable}`;
}

Best Practices for Production

• Escape LaTeX special characters before any other processing: The characters _ & % $ # { } ~ ^ \ all have meaning in LaTeX. Escape them first, before adding any LaTeX markup like \textbf{}. If you do it after, you'll double-escape the markup you just inserted.
• Use booktabs and never use vertical lines: The style guide for academic tables is unanimous: use \toprule, \midrule, \bottomrule from the booktabs package. Never use vertical lines or \hline. This is also the style required by most journal templates (IEEE, ACM, Springer).
• Use siunitx S columns for all numeric data: Manual alignment with spaces or phantom{} is fragile and doesn't handle varying decimal places. The S column type aligns at the decimal point automatically and allows table-format to specify width. Headers in S columns must be wrapped in {braces} to prevent siunitx from treating them as numbers.
• Generate \label and \caption from JSON metadata: Include a caption and label field in your JSON data definition. The \label{tab:...} enables \ref{tab:...} cross-references in the document. Consistent label naming (e.g., tab:slug-name) prevents duplicate labels when generating multiple tables.

FAQ

Q: How do I bold the maximum value in each column?
A: Two-pass approach: first scan all data to find the max per column, then generate LaTeX wrapping max values with \textbf{}. For numeric S columns, wrap the number: \textbf{88.7} still aligns correctly in siunitx.

Q: How do I include a table in a LaTeX document from a generated .tex file?
A: Use \input{tables/benchmarks.tex} in your main document. The generator writes just the table environment (not a full document), which is included inline. Run the generator as a pre-build step: node scripts/gen-tables.js && pdflatex main.tex.

Q: How do I generate tables for IEEE or ACM conference templates?
A: Both templates include booktabs and allow custom packages. Use \usepackage{booktabs} and \usepackage{siunitx} in the preamble. IEEE templates use IEEEtable for wide tables spanning both columns; replace table with table* in your generator for double-column float mode.