Converting between xarray and dataset should convert attrs types better

[ctrueden]

>>> import imagej
>>> ij = imagej.init()
>>> d = ij.io().open('/home/curtis/data/blobs.tif')
>>> d
<java object 'net.imagej.DefaultDataset'>
>>> ij.py.from_java(d)
<xarray.DataArray (row: 254, col: 256)>
array([[ 40,  32,  24, ..., 216, 200, 200],
       [ 56,  40,  24, ..., 232, 216, 216],
       [ 64,  48,  24, ..., 240, 232, 232],
       ...,
       [ 72,  80,  80, ...,  48,  48,  48],
       [ 80,  80,  80, ...,  48,  48,  48],
       [ 96,  88,  80, ...,  48,  48,  48]], dtype=uint8)
Coordinates:
  * row      (row) float64 0.0 1.0 2.0 3.0 4.0 ... 249.0 250.0 251.0 252.0 253.0
  * col      (col) float64 0.0 1.0 2.0 3.0 4.0 ... 251.0 252.0 253.0 254.0 255.0
Attributes:
    rois:                    None
    tables:                  None
    scifio.metadata.image:   io.scif.FieldPrinter@661c46bc\n\t--class io.scif...
    scifio.metadata.global:  io.scif.filters.PlaneSeparatorMetadata@37864b77

Note poor stringification of scifio.metadata.image and scifio.metadata.global data structures above.

See also spatial-image/multiscale-spatial-image#23

[gselzer]

@ctrueden what does "better" mean in this context? We already call sj.to_python on the properties...
If we're talking about the metadata, what would you want to see? Does xarray offer settings aligning with this metadata?

Do you just want to see a better stringification? Or would you want to convert these properties into dicts?

[ctrueden]

what does "better" mean in this context?

Here's what I wrote in the discussion thread of spatial-image/multiscale-spatial-image#23:

My goal with #200 would be to eliminate the need to do this. If a Java-side attribute can't be converted to something Pythonic, I think it's OK to drop it. We could at least make it configurable somehow.

So, behavior in order of priority:

1. Convert property value into something Pythonic.
2. Drop properties which cannot be converted.

The remaining question is just: can io.scif.FieldPrinter and io.scif.filters.PlaneSeparatorMetadata be converted? I'm pretty confident that FieldPrinter can be converted; the entire point of that class was to ease printing of key/value pairs. We probably just need to implement a toString() method somewhere on the Java side. For PlaneSeparatorMetadata I don't know off the top of my head; investigation needed.