Summing it up: Aggregating repeating nodes in Logic Apps Data Mapper 🧮

Logic Apps Data Mapper makes it easy to define visual, code-free transformations across structured JSON data. One pattern that's both powerful and clean: using built-in collection functions to compute summary values from arrays.

This post walks through an end-to-end example: calculating a total from a list of items using just two functions — `Multiply` and `Sum`.

🧾 Scenario: Line Item Totals + Order Summary

You’re working with a list of order items. For each item, you want to:

• Compute Total = Quantity × Price
• Then, compute the overall OrderTotal by summing all the individual totals

📥 Input

{ "orders" : [ { "Quantity" : 10, "Price" : 100 }, { "Quantity" : 20, "Price" : 200 }, { "Quantity" : 30, "Price" : 300 } ] }

📤 Output

{ "orders" : [ { "Quantity" : 10, "Price" : 100, "Total" : 1000 }, { "Quantity" : 20, "Price" : 200, "Total" : 4000 }, { "Quantity" : 30, "Price" : 300, "Total" : 9000 } ], "Summary": { "OrderTotal": 14000 } }

🔧 Step-by-step walkthrough

🗂️ 1. Load schemas in Data Mapper

Start in the Azure Data Mapper interface and load:

• Source schema: contains the orders array with Quantity and Price
• Target schema: includes a repeating orders node and a Summary → OrderTotal field

📸 Docked schemas in the mapper

🔁 2. Recognize the repeating node

The orders array shows a 🔁 icon on <ArrayItem>, marking it as a repeating node.
📸 Repeating node detection

💡 When you connect child fields like Quantity or Price, the mapper auto-applies a loop for you. No manual loop configuration needed.

➗ 3. Multiply Quantity × Price (per item)

Drag in a Multiply function and connect:

• Input 1: Quantity
• Input 2: Price

Now connect the output of Multiply directly to the Total node under Orders node in the destination.

This runs once per order item and produces individual totals:

[1000, 4000, 9000]

📸 Multiply setup

➕ 4. Aggregate All Totals Using Sum

Use the same Multiply function output and pass it into a Sum function. This will combine all the individual totals into one value. Drag and connect: 

• Input 1: multiply(Quantity, Price)
• Input 2: <ArrayItem>

Connect the output of Sum to the destination node Summary → OrderTotal

1000 + 4000 + 9000 = 14000

📸 Sum function

✅ 5. Test the Output

Run a test with your sample input by clicking on the Open test panel. Copy/paste the sample data and hit Test. 

The result should look like this:

{
  "orders": [
    {
      "Quantity": 10,
      "Price": 100,
      "Total": 1000
    },
    {
      "Quantity": 20,
      "Price": 200,
      "Total": 4000
    },
    {
      "Quantity": 30,
      "Price": 300,
      "Total": 9000
    }  
  ],
  "Summary": {
    "OrderTotal": 14000
  }
}

🧠 Why this pattern works

• 🔁 Repeating to repeating: You’re calculating Total per order
• 🔂 Repeating to non-repeating: You’re aggregating with Sum into a single node
• 🧩 No expressions needed — it’s all declarative

This structure is perfect for invoices, order summaries, or reporting payloads where both detail and summary values are needed.

📘 What's coming

We’re working on official docs to cover:

• All functions including collection (Join, Direct Access, Filter, etc.) that work on repeating nodes
• Behavior of functions inside loops
• Real-world examples like this one

💬 What should we cover next?

We’re always looking to surface patterns that matter most to how you build.

If there’s a transformation technique, edge case, or integration scenario you’d like to see explored next — drop a comment below and let us know. We’re listening.

🧡 Special thanks to Dave Phelps for collaborating on this scenario and helping shape the walkthrough.