Aggregate Multiple Items into a Single Summary Using the Aggregate Node

The Aggregate node collapses multiple items into one, which is the inverse of Split Out. Use it when you need to collect results from a loop or batch and produce a single summary object -- for example, to compose one email with all line items.

Real-world example: A workflow processes 15 order line items individually (for inventory checks). Now you need to combine them into a single summary for a confirmation email.

Configure the Aggregate node:

Setting	Value
Aggregate	Individual Fields
Input Field	product_name -> Output: products
Input Field	line_total -> Output: amounts

// Input — 3 items:
{ "product_name": "Widget A", "line_total": 29.99, "qty": 2 }
{ "product_name": "Widget B", "line_total": 49.99, "qty": 1 }
{ "product_name": "Widget C", "line_total": 15.00, "qty": 5 }

// Aggregated output — 1 item:
{
  "products": ["Widget A", "Widget B", "Widget C"],
  "amounts": [29.99, 49.99, 15.00]
}
```text
Follow up with a Code node to build the email body:

```javascript
const products = $json.products;
const amounts = $json.amounts;
const total = amounts.reduce((sum, val) => sum + val, 0);

let body = "Order Summary:\n\n";
for (let i = 0; i < products.length; i++) {
  body += `- ${products[i]}: $${amounts[i].toFixed(2)}\n`;
}
body += `\nTotal: $${total.toFixed(2)}`;

return [{ json: { emailBody: body, orderTotal: total } }];
```text
The email node then receives a single item with a fully composed body instead of 15 individual fragments.

**Related:** [Flatten Deeply Nested API Responses](../code-node-mastery/01-flatten-deeply-nested-api-responses.md) | [Use the HTTP Request Node as a Universal Connector](../integration-patterns/01-use-the-http-request-node-as-a-universal-connector.md)