Power Automate Loop Sum Self Reference Is Not Supported

Power Automate Loop: Summing Values - Why Self-Reference Fails and How to Solve It

Power Automate is a powerful tool for automating workflows, but sometimes you encounter limitations. One common issue arises when attempting to sum values within a loop using a self-referencing approach. This article explains why this method fails and provides practical solutions to efficiently sum values within your Power Automate flows. Understanding this will help you build robust and accurate automation processes.

The Problem: Why Self-Reference Doesn't Work

The core issue stems from the way Power Automate handles variables within loops. When you try to use a variable inside a loop to accumulate a sum by referencing the variable itself within the loop's action (like adding to the current value of the variable), you'll run into the "self-reference is not supported" error. This is because Power Automate's loop engine needs to fully resolve variable values before the loop's next iteration begins. Trying to update the same variable within the loop's iteration before the iteration is complete creates a circular dependency that the engine cannot resolve.

Understanding the Limitation

Imagine a scenario where you're trying to sum numbers from an array. A naive approach might be to use a variable initialized to zero and add each array element to it within the loop. This approach won't work because the engine can't handle the immediate update of the variable during the loop's execution cycle.

Solution 1: Using Initialize Variable and Compose Actions

This is the most straightforward solution. We'll use an "Initialize variable" action to start with a sum of 0. Then, inside the loop, a "Compose" action will calculate the sum for the current iteration. Finally, after the loop, you'll have the total.

1. Initialize Variable: Create a variable (e.g., totalSum) and set its initial value to 0.
2. Apply to each: Loop through your array of numbers.
3. Compose: Inside the loop, use a Compose action with the expression: int(variables('totalSum')) + int(item()). This adds the current item's value to the existing totalSum. The int() function ensures we are working with numbers.
4. Set Variable: After the Compose action, use a "Set variable" action to update totalSum with the output from the Compose action.
5. Access the total: After the loop, the totalSum variable will contain the sum of all numbers in the array.

Solution 2: Using the sum() Function (For Arrays)

If you're working directly with an array of numbers, the most efficient solution is to use the built-in sum() function outside of a loop. This eliminates the need for looping entirely.

1. Get the array: Retrieve your array of numbers.
2. Sum the array: Use a "Compose" action with the expression: sum(body('Get_array')). Replace 'Get_array' with the actual name of your array output.

Solution 3: Using a Collection (For More Complex Scenarios)

For more intricate scenarios involving complex data structures, consider using a collection. You can append values to a collection within the loop and then sum the collection's values afterward. This approach provides greater flexibility when dealing with intricate data manipulation within the loop.

1. Initialize a collection: Use the "Initialize variable" action to create an empty collection.
2. Append to each: Use the "Append to array variable" action to add numbers from your data to the collection within the loop.
3. Sum the collection: After the loop, use a "Compose" action with a formula to sum the values within the collection (using the sum() function).

Choosing the Right Solution

The best solution depends on your specific needs and the structure of your data. For simple arrays of numbers, the sum() function is the most elegant and efficient. For more complex scenarios or when you need to perform other calculations within the loop alongside the summation, using an "Initialize Variable," "Compose," and "Set Variable" actions, or a collection, provides the necessary control. Avoid directly updating a variable within the loop's iteration itself to avoid the self-reference error. Remember to always test thoroughly after implementing any solution.