Move to using getproperty for accessing RasterStack layers?

[rafaqz]

It would be nice if we could use Symbol and String to to access categorical variables in DimensionalData.jl and inheriting packages, without wrapping them with At. But there are some edge cases where that clashes with DimStack/RasterStack getindex syntax, and will effect users of Rasters.jl the most.

rafaqz/DimensionalData.jl#338 (comment)

The problem generally is that DimStack/RasterStack overloads the Array/NamedTuple combination, in ways that are sometimes confusing, but also pretty powerful. Currently we use getindex of a single Symbol to retrieve a stack layer, and any other getindex to retrieve the values of all of the Raster layers, or slice them all.

I'm considering migrating the syntax to getproperty, like this:

rasterstack[:layername]
# To
rasterstack.layername

Then rasterstack[args...] is always indexing the values of the layers, and never fetching a layer (after a period of depreciation)

There are probably a few more changes like this that need to happen, because as @mkborregaard has said, RasterStack getindex is pretty weird - first(rasterstack) returns a single Raster layer while rasterstack[1] returns a NamedTuple of the first value of all the layers !!!. This is because iteration happens over whole layers, like a NamedTuple of Array, but for getindex a stack is is like an Array of NamedTuple.

We might need to contain that weirdness somehow. One option is to not use getindex for retrieving values at all, which resolves the problem. But then you can't do:

rasterstack[X=Between(100, 160), Y=Between(0, 40)]

Which is one of the main things I do with a RasterStack after loading a netcdf. If anyone has any thoughts or feedback, that would be great, I don't want to break everyones workflow unless it makes sense.

@vlandau @mauro3 @mkborregaard @jamesmaino @virgile-baudrot

[jamesmaino]

I'm trying hard to remember back to when we first discussed this weirdness. I think I was advocating hyperdimensional arrays where time is an index but there were issues with that setup too. We never thought of using the getproperty syntax. Definitely a big change though...

What would be the alternative for rasterstack[X=Between(100, 160), Y=Between(0, 40)]?

[rafaqz]

I never thought about it before either, I just realised the other day that its actually the main way to index a NamedTuple, and that's pretty much what a stack is. (I think we were discussing just mushing all of the indexing into one flat getindex even for RasterSeries... just to make things even weirder. But I'm kind of glad we didn't... slice/combine make that kind of redundant now, and they are quite ordinary in comparison.)

I don't know what an alternative to that getindex example could be, I really like it as-is honestly, and that its exactly the same as for an array. Others seem to as well, @maxfreu wanted to use RasterStack specifically because its so easy to index multiple layers at once.

Maybe we could use another function name for indexing stacks, but the [ ] brackets are hard to beat for style.

[rafaqz]

Completed