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How to Subtract Array Values by Index in Power Automate for Desktop

Algirdas Jasaitis Oct 1, 2026 869 views

Question details

The user needs to calculate the difference between matching values stored in two separate arrays by using a variable index.

How to Subtract Array Values by Index in Power Automate for Desktop

Product: Power Automate for Desktop
Device & OS: not provided
Scenario: Extracting text from a PDF, storing the numerical positions of specific phrases into arrays, and subtracting one array's values from another.
Observed behavior: The user is looking for the correct syntax and logic to access array elements via an index variable and perform the subtraction.

Before you start

Ensure you have successfully extracted the PDF text and that both arrays are populated with numerical position values before setting up the subtraction logic.

Solution 1Recommended

Use a Loop Counter for Array Subtraction

Utilize a loop counter variable to iterate through the arrays, retrieve corresponding elements by their index, and calculate their difference.

To subtract values stored in two different arrays, you must use a shared index. Since Power Automate for Desktop processes lists sequentially, a standard loop configuration allows you to reference the exact position in both arrays simultaneously.

Initialize a Loop

Add a 'Loop' action to your flow. Set the 'Start from' value to 0, and the 'End to' value to `%Array1.Count - 1%`. Name the loop variable `%LoopIndex%`.

Retrieve Array Values

Inside the loop, use the syntax `%Array1[LoopIndex]%` and `%Array2[LoopIndex]%` to access the specific positional values you extracted from the PDF.

Perform Subtraction

Add a 'Set variable' action inside the loop. In the value field, enter the expression `%Array2[LoopIndex] - Array1[LoopIndex]%` to calculate the difference and store it in a new variable.

Use a Loop Counter for Array Subtraction

Syntax Validation: If you receive a syntax error, ensure that your array values are stored as numbers rather than text strings. You may need to use the 'Convert text to number' action first.

Solution 2

Consult the Power Automate Community for Advanced Syntax

If you encounter complex variable type errors during flow execution, consult flow specialists on the official Microsoft forums.

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Frequently Asked Questions

Why am I getting an out-of-bounds error when accessing the array?

This error occurs if your loop counter exceeds the number of items stored in the array. Ensure your loop condition ends at `%Array.Count - 1%` since Power Automate arrays are zero-indexed.

Can I subtract array values directly without a loop in Power Automate?

No, Power Automate for Desktop does not support direct matrix or array-level arithmetic natively. You must iterate through the arrays using a loop or run a custom script (like VBScript or Python) to process the elements.

How do I ensure my array values are treated as numbers instead of text?

When extracting text from a PDF, the values are often stored as string data types. Use the 'Convert text to number' action in your flow on each array element before attempting to perform mathematical subtraction.

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