Make changes for datasets with only one file (#335)

* Test scalar array to filename

* Make changes for datasets with only one file

This is towards fixing VBI single shot mosaics

* Add changelog

---------

Co-authored-by: Drew Leonard <[email protected]>

changelog/335.trivial.rst

@@ -0,0 +1 @@
+Adjust file loading to support single-frame datasets with no time axis.

dkist/conftest.py

@@ -228,7 +228,9 @@ def dataset(array, identity_gwcs):
     assert ds.data is array
     assert ds.wcs is identity_gwcs
 
-    ds._file_manager = FileManager.from_parts(['test1.fits'], 0, 'float', array.shape,
+    # Construct the filename here as a scalar array to make sure that works as
+    # it's what dkist-inventory does
+    ds._file_manager = FileManager.from_parts(np.array('test1.fits'), 0, 'float', array.shape,
                                               loader=AstropyFITSLoader)
 
     return ds

dkist/io/dask_utils.py

@@ -23,6 +23,8 @@ def stack_loader_array(loader_array, chunksize):
     # If the chunksize sin't specified then use the whole array shape
     chunksize = chunksize or loader_array.flat[0].shape
 
+    if loader_array.size == 1:
+        return tuple(loader_to_dask(loader_array, chunksize))[0]
     if len(loader_array.shape) == 1:
         return da.stack(loader_to_dask(loader_array, chunksize))
     stacks = []
@@ -38,10 +40,11 @@ def loader_to_dask(loader_array, chunksize):
     This is done so that an explicit ``meta=`` argument can be provided to
     prevent loading data from disk.
     """
-
-    if len(loader_array.shape) != 1:
+    if loader_array.size != 1 and len(loader_array.shape) != 1:
         raise ValueError("Can only be used on one dimensional arrays")
 
+    loader_array = np.atleast_1d(loader_array)
+
     # The meta argument to from array is used to determine properties of the
     # array, such as dtype. We explicitly specify it here to prevent dask
     # trying to auto calculate it by reading from the actual array on disk.

dkist/io/file_manager.py

@@ -56,7 +56,7 @@ def _output_shape_from_ref_array(shape, loader_array) -> Tuple[int]:
         if shape[0] == 1:
             shape = shape[1:]
 
-        if len(loader_array) == 1:
+        if loader_array.size == 1:
             return shape
         else:
             return tuple(list(loader_array.shape) + list(shape))
@@ -99,8 +99,7 @@ def __init__(
         self._basepath = None
         self.basepath = basepath  # Use the setter to convert to a Path
         self.chunksize = chunksize
-
-        self._fileuri_array = np.array(fileuris)
+        self._fileuri_array = np.atleast_1d(np.array(fileuris))
 
         loader_array = np.empty_like(self._fileuri_array, dtype=object)
         for i, fileuri in enumerate(self._fileuri_array.flat):