tidy-eval summarise

[zackarno]

just posting this here so we dont forget @joshualerickson ....
want to add some flexibility to summarise with tidyeval.

We can use this page to add some examples and ideas

[zackarno]

Had a conceptual idea on how this might work. Would also be the same for mutate transformations:

We currently have bands stored as list-col in the vrt - useful for the tidyee print method, but not much else. It could make sense to store each band as a column in the vrt which would supply us with bindings to do whatever we want inside mutate/summarise and translate that to the image/collection.

What to store in the band columns though? I think it probably makes sense to store some sort of "pre-compute" / "empty" default. If the user wants they can choose to run some functions to run a computation to actually compute some values for those bands for each image- maybe some estimated summary stats would make sense (something useful for viz). However, leaving them basically empty as a default seems like it could be a good idea since any calculation might end up being a bit expensive on an entire imagecollection. I haven't been able to think of any other simple way to add this functionality which would be awesome to have and not positive this would work.

thoughts @joshualerickson ?