r-novice-inflammation | Programming with R

I am fairly new to R, and have spent a long time looking for a better way to solve my issue below with no success. I was able to develop a solution using for loops that works; however, I am breaking the rules described on this GitHub tutorial discussing what to avoid when writing loops.

I am working with sales data. My particular data frame includes Product Categories ("CAT_NO"), Customer Deciles ("CUST_DECILE") (customers are placed into a Decile group from 1 to 10, with 1 being the "best" customers) and floor gross margins ("floorGM") for that Product Category, Customer Decile combination. It may be worth noting that not every Product Category will have all Customer Deciles represented (e.g., Sample Category "A" may only have Customer Deciles 4, 7, and 9. For simplicity purposes, the reproducible example below ensures that each Product Category has all 10 Customer Deciles). My data set can be represented by: