Support loading histogram monitors

Author: jl-wynen

src/ess/reduce/data.py

@@ -40,6 +40,15 @@ def get_path(self, name: str, unzip: bool = False) -> str:
 )
 
 
+_dream_registry = Registry(
+    instrument='dream',
+    files={
+        "TEST_977695_00068064.hdf": "md5:9e6ee9ec70d7c5e8c0c93b9e07e8949f",
+    },
+    version='2',
+)
+
+
 _loki_registry = Registry(
     instrument='loki',
     files={
@@ -94,3 +103,11 @@ def loki_tutorial_background_run_60393() -> str:
 def loki_tutorial_sample_transmission_run() -> str:
     """Sample transmission run (sample + sample holder/can + transmission monitor)."""
     return _loki_registry.get_path('60394-2022-02-28_2215.nxs')
+
+
+def dream_coda_test_file() -> str:
+    """CODA file for DREAM where most pulses have been removed.
+
+    See ``tools/shrink_nexus.py``.
+    """
+    return _dream_registry.get_path('TEST_977695_00068064.hdf')

src/ess/reduce/nexus/workflow.py

@@ -560,10 +560,10 @@ def __init__(
 class _DummyField:
     """Dummy field that can replace snx.Field in NXmonitor."""
 
-    def __init__(self):
+    def __init__(self, dim: str):
         self.attrs = {}
-        self.sizes = {'event_time_zero': 0}
-        self.dims = ('event_time_zero',)
+        self.sizes = {dim: 0}
+        self.dims = (dim,)
         self.shape = (0,)
 
     def __getitem__(self, key: Any) -> sc.Variable:
@@ -573,14 +573,17 @@ def __getitem__(self, key: Any) -> sc.Variable:
 class _StrippedMonitor(snx.NXmonitor):
     """Monitor definition without event data for ScippNexus.
 
-    Drops NXevent_data group, data is replaced by a dummy field.
+    Drops NXevent_data and NXdata groups, data is replaced by a dummy field.
     """
 
     def __init__(
         self, attrs: dict[str, Any], children: dict[str, snx.Field | snx.Group]
     ):
-        children = _drop(children, (snx.NXevent_data,))
-        children['data'] = _DummyField()
+        is_dense = snx.NXdata in (
+            getattr(child, 'nx_class', None) for child in children
+        )
+        children = _drop(children, (snx.NXevent_data, snx.NXdata))
+        children['data'] = _DummyField(dim='time' if is_dense else 'event_time_zero')
         super().__init__(attrs=attrs, children=children)
 
 
@@ -590,6 +593,12 @@ def _add_variances(da: sc.DataArray) -> sc.DataArray:
         content = out.bins.constituents['data']
         if content.variances is None:
             content.variances = content.values
+    elif out.variances is None:
+        try:
+            out.variances = out.values
+        except sc.VariancesError:
+            out = out.to(dtype=sc.DType.float64)
+            out.variances = out.values
     return out
 
 

tests/nexus/workflow_test.py

@@ -471,6 +471,21 @@ def monitor_event_data() -> workflow.NeXusData[FrameMonitor1, SampleRun]:
     )
 
 
+@pytest.fixture
+def monitor_histogram_data() -> workflow.NeXusData[FrameMonitor1, SampleRun]:
+    time = sc.epoch(unit='ns') + sc.arange('time', 1, 6, unit='s').to(unit='ns')
+    frame_time = sc.arange('frame_time', 12, unit='ms').to(unit='ns')
+    return workflow.NeXusData[FrameMonitor1, SampleRun](
+        sc.DataArray(
+            10.0
+            * sc.arange('x', 5 * 12, unit='counts').fold(
+                'x', sizes={'time': 5, 'frame_time': 12}
+            ),
+            coords={'time': time, 'frame_time': frame_time},
+        )
+    )
+
+
 def test_assemble_monitor_data_adds_events_as_values_and_coords(
     calibrated_monitor, monitor_event_data
 ) -> None:
@@ -482,7 +497,7 @@ def test_assemble_monitor_data_adds_events_as_values_and_coords(
     )
 
 
-def test_assemble_monitor_data_adds_variances_to_weights(
+def test_assemble_monitor_data_adds_variances_to_events(
     calibrated_monitor, monitor_event_data
 ) -> None:
     monitor_data = workflow.assemble_monitor_data(
@@ -494,6 +509,30 @@ def test_assemble_monitor_data_adds_variances_to_weights(
     )
 
 
+def test_assemble_monitor_data_adds_histogram_as_values_and_coords(
+    calibrated_monitor, monitor_histogram_data
+) -> None:
+    monitor_data = workflow.assemble_monitor_data(
+        calibrated_monitor, monitor_histogram_data
+    )
+    assert_identical(
+        monitor_data.drop_coords(tuple(calibrated_monitor.coords)),
+        monitor_histogram_data,
+    )
+
+
+def test_assemble_monitor_data_adds_variances_to_weights(
+    calibrated_monitor, monitor_histogram_data
+) -> None:
+    monitor_data = workflow.assemble_monitor_data(
+        calibrated_monitor, monitor_histogram_data
+    )
+    assert_identical(
+        sc.variances(monitor_data.drop_coords(tuple(calibrated_monitor.coords))),
+        monitor_histogram_data,
+    )
+
+
 def test_assemble_monitor_preserves_coords(calibrated_monitor, monitor_event_data):
     calibrated_monitor.coords['abc'] = sc.scalar(1.2)
     monitor_data = workflow.assemble_monitor_data(
@@ -510,7 +549,7 @@ def test_assemble_monitor_preserves_masks(calibrated_monitor, monitor_event_data
     assert 'mymask' in monitor_data.masks
 
 
-def test_load_monitor_workflow() -> None:
+def test_load_event_monitor_workflow() -> None:
     wf = LoadMonitorWorkflow(run_types=[SampleRun], monitor_types=[FrameMonitor1])
     wf[Filename[SampleRun]] = data.loki_tutorial_sample_run_60250()
     wf[NeXusName[FrameMonitor1]] = 'monitor_1'
@@ -519,6 +558,21 @@ def test_load_monitor_workflow() -> None:
     assert 'source_position' in da.coords
     assert da.bins is not None
     assert da.dims == ('event_time_zero',)
+    assert da.bins.constituents['data'].variances is not None
+
+
+def test_load_histogram_monitor_workflow() -> None:
+    wf = LoadMonitorWorkflow(run_types=[SampleRun], monitor_types=[FrameMonitor1])
+    wf[Filename[SampleRun]] = data.dream_coda_test_file()
+    wf[NeXusName[FrameMonitor1]] = 'monitor_bunker'
+    da = wf.compute(MonitorData[SampleRun, FrameMonitor1])
+    assert 'position' in da.coords
+    assert 'source_position' in da.coords
+    assert da.bins is None
+    assert da.dims == ('time', 'frame_time')
+    assert 'time' in da.coords.keys()
+    assert 'frame_time' in da.coords.keys()
+    assert da.variances is not None
 
 
 def test_load_detector_workflow() -> None: