How to Create a Spilled Excel Array for Forecast Month Totals
Question details
The user needs to calculate cumulative values for each row by summing a dynamic number of forecast months using a single spilled array formula.
- Product
- Excel
- Device & OS
- not provided
- Scenario
- Calculating row-by-row totals simultaneously based on a variable number of forecast months specified in the source data without manually dragging formulas.
- Observed behavior
- A single spilled formula is required to output cumulative totals dynamically across multiple rows, adapting to different month values per row.
Ensure that your spreadsheet software supports dynamic array functions like BYROW and LAMBDA, and verify that the intended output range is completely empty to prevent a #SPILL! error.
Use the BYROW and LAMBDA Functions for a Dynamic Array
This method utilizes modern dynamic arrays to calculate row-by-row totals simultaneously using a single spilled formula.
By combining the BYROW function with a custom LAMBDA formula, you can iterate through an array of specified month values. The CHOOSECOLS and SEQUENCE functions are then used to dynamically select the correct number of months to sum for each respective row.
Click on the uppermost cell where you want the cumulative totals to begin displaying (for example, cell N2).
Type the formula =BYROW(A2:A7,LAMBDA(months,SUM(CHOOSEROWS(CHOOSECOLS(B2:M7,SEQUENCE(months)),ROWS(A2:A7))))) into the formula bar. Adjust the ranges A2:A7 (forecast months) and B2:M7 (data grid) to match your specific workbook layout.
Press the Enter key. The results will automatically spill down the column, providing the correct sum for each row based on its specific forecast-month value.
Calculate Totals Using the OFFSET Function
An alternative method that relies on the OFFSET function to define the dynamic range of columns to sum.
Calculate Dynamic Forecast Totals in WPS Spreadsheet
WPS Spreadsheet fully supports modern dynamic array formulas, allowing you to easily manage spilled arrays for complex data calculations like forecast month totals.
- 1. Open your workbook in WPS: Launch WPS Spreadsheet and open the file containing your forecast source data.
- 2. Select the output cell: Click the completely empty cell where you want the spilled array to start.
- 3. Apply the array formula: Enter the BYROW and LAMBDA formula tailored to your data range, then press Enter to instantly generate the spilled totals.
Frequently Asked Questions
Why am I getting a #SPILL! error when entering the array formula?
A #SPILL! error occurs when the formula needs to output results into multiple cells, but one or more of those target cells already contain data, spaces, or formatting. Clear the entire column below your formula cell to resolve this.
Can I use LAMBDA and BYROW in older spreadsheet versions?
No, LAMBDA and BYROW are modern dynamic array functions. If you are using an older version of Excel or other spreadsheet software that hasn't been updated, you will need to use traditional drag-down formulas like the OFFSET method.
How do I update the number of forecast months for a specific row?
Simply change the integer value in the designated forecast-month column (e.g., changing the value in A3 from 3 to 5). Because the spilled array formula calculates dynamically, the total for that specific row will automatically update.
