The problem is very simple. Everybody understands how to sum cell A1 with cell B1 and have a result in cell C1. Summing arrays, though, like in an R dataframe,

The problem is very simple. Everybody understands how to sum cell A1 with cell B1 and have a result in cell C1. Summing arrays, though, like in an R dataframe, is much more difficult to understand. You don't see it and you need to train your brain to think in SQL terms.