Use Google Apps Script to Autofill a formula down rows in a Google Sheet.
The following Google Apps Script is designed to insert a formula into the first row of data in a Google Sheet, then use Autofill to add the formula to the subsequent rows below. In this example I am just using a simple Sum formula to add up age and shoesize for demo purposes. The need to do this came about when combining multiple Google Sheet files however, that needed calculations adding to the final composed version.
I use Google Apps Script to support staff and students in my job. I enjoy dabbling with creating tools to help with automation and I freely share my learning experiences on my blog, where I also have a number of useful Google Add-ons: www.pbainbridge.co.uk