Add functionality to "summarise across" columns

[nikosbosse]

If you have forecast for different dates, locations, models, and horizons. And you want to get scores averaged over dates, then you have to do something like summarise_scores(by = c("model", "location", "horizon"). It could be nice to also allow the opposite way to just say: summarise_scores(across = "horizon") and it would just keep the forecast unit as is and automatically translate that into the first statement.
For people who know what they do this could be nice. For others, it might be confusing...

[seabbs]

I can see why experienced uses might want this. Personally I always manually specify by as I find the forecast unit determination a bit of a mystery.

I would come down against this just because of the additional code complexity but I am very open to it if people think it would be useful.