Aggregate Data Across All Items With `$input.all()`

To aggregate data across every item in n8n, run a Code node in "Run Once for All Items" mode and iterate over $input.all(). Reduce the items into a single object holding totals and grouped breakdowns, and return it as one item. This is more reliable than accumulating values across a loop with the Set node.

What does $input.all() do in n8n?

When you need to compute summaries, totals, or grouped statistics across every item in a batch, use $input.all() in "Run Once for All Items" mode. This is far more reliable than trying to accumulate values across a loop using the Set node.

Real-world example: After fetching all invoice line items from QuickBooks, you need to produce a summary with total revenue, tax collected, and a breakdown by product category.

How do you aggregate data across all items with $input.all()?

// Mode: Run Once for All Items
const items = $input.all().map(i => i.json);

const summary = items.reduce((acc, line) => {
  acc.totalRevenue += line.amount;
  acc.totalTax += line.taxAmount ?? 0;
  acc.itemCount += 1;

  const cat = line.category || 'Uncategorized';
  if (!acc.byCategory[cat]) {
    acc.byCategory[cat] = { revenue: 0, count: 0 };
  }
  acc.byCategory[cat].revenue += line.amount;
  acc.byCategory[cat].count += 1;

  return acc;
}, { totalRevenue: 0, totalTax: 0, itemCount: 0, byCategory: {} });

// Convert byCategory to an array for easier downstream use
summary.categoryBreakdown = Object.entries(summary.byCategory).map(
  ([name, data]) => ({ category: name, ...data })
);
delete summary.byCategory;

return [{ json: summary }];

The output is a single item containing the full summary, ready to be inserted into a dashboard, sent in a report email, or stored in a database.

When should you use "Run Once for All Items" mode?

• You need summaries, totals, or grouped statistics computed across every item in a batch.
• You would otherwise accumulate values across a loop with the Set node, which is far less reliable.

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