The docs for Apps Script are pretty good: https://developers.google.com/apps-script https://developers.google.com/apps-script Start here for custom functions:

The docs for Apps Script are pretty good: https://developers.google.com/apps-script https://developers.google.com/apps-script Start here for custom functions: https://developers.google.com/apps-script/quickstart/custom-functions https://developers.google.com/apps-script/quickstart/custom-... Array functions are weird in scripts, but just playing around with them should help understand how they work.