[ESSdiffraction] Save XYE files in tests and apply masks

packages/essdiffraction/src/ess/dream/io/__init__.py

@@ -5,7 +5,8 @@
 
 from .cif import prepare_reduced_tof_cif
 from .geant4 import load_geant4_csv
+from .xye import save_xye
 
 providers = (prepare_reduced_tof_cif,)
 
-__all__ = ["load_geant4_csv", "prepare_reduced_tof_cif", "providers"]
+__all__ = ["load_geant4_csv", "prepare_reduced_tof_cif", "providers", "save_xye"]

packages/essdiffraction/src/ess/dream/io/_common.py

@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2026 Scipp contributors (https://github.com/scipp)
+
+import scipp as sc
+from scipp.core import irreducible_mask
+
+
+def prepare_reduced_data(da: sc.DataArray) -> sc.DataArray:
+    """Prepare reduced data for saving."""
+    if da.ndim != 1:
+        raise sc.DimensionError(f"Can only save 1D data, got {da.sizes}")
+
+    hist = da.hist() if da.is_binned else da.copy(deep=False)
+    hist.coords[hist.dim] = sc.midpoints(hist.coords[hist.dim])
+
+    if hist.masks:
+        # No file format we use here supports masks, so the next
+        # best thing is to zero out masked data:
+        hist.data = hist.data.copy()
+        hist.values *= irreducible_mask(hist.masks, hist.dim).values
+        hist.masks.clear()
+
+    return hist

packages/essdiffraction/src/ess/dream/io/cif.py

@@ -1,9 +1,8 @@
 # SPDX-License-Identifier: BSD-3-Clause
-# Copyright (c) 2023 Scipp contributors (https://github.com/scipp)
+# Copyright (c) 2026 Scipp contributors (https://github.com/scipp)
 
 """CIF writer for DREAM."""
 
-import scipp as sc
 from ess.powder.calibration import OutputCalibrationData
 from ess.powder.types import (
     Beamline,
@@ -19,6 +18,8 @@
 )
 from scippneutron.io import cif
 
+from ._common import prepare_reduced_data
+
 
 def prepare_reduced_tof_cif(
     da: IntensityTof,
@@ -126,7 +127,7 @@ def _prepare_reduced_tof_cif_impl(
     reducers: ReducerSoftware,
     calibration: OutputCalibrationData,
 ) -> ReducedTofCIF:
-    to_save = _prepare_data(da)
+    to_save = prepare_reduced_data(da)
     return ReducedTofCIF(
         cif.CIF('reduced_tof')
         .with_measurement(measurement)
@@ -136,9 +137,3 @@ def _prepare_reduced_tof_cif_impl(
         .with_powder_calibration(calibration.to_cif_format())
         .with_reduced_powder_data(to_save)
     )
-
-
-def _prepare_data(da: sc.DataArray) -> sc.DataArray:
-    hist = da.copy(deep=False) if da.bins is None else da.hist()
-    hist.coords[hist.dim] = sc.midpoints(hist.coords[hist.dim])
-    return hist

packages/essdiffraction/src/ess/dream/io/xye.py

@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2026 Scipp contributors (https://github.com/scipp)
+
+"""XYE writer for DREAM."""
+
+import scippneutron as scn
+from ess.powder.types import IntensityTof, OutFilename
+
+from ._common import prepare_reduced_data
+
+
+def save_xye(filename: OutFilename, da: IntensityTof) -> None:
+    """Save reduced data to an XYE file.
+
+    This function can be used as
+
+    .. code-block:: python
+
+        from ess.powder.types import OutFilename
+        from ess.dream.io import save_xye
+
+        workflow = ...
+        workflow[OutFilename] = "..."
+        workflow.bind_and_call(save_xye)
+
+    Note that this function is not suitable as a provider as it
+    has side effects (writes a file).
+
+    Parameters
+    ----------
+    filename:
+        Path of a file to write to.
+    da:
+        Reduced 1d data with a ``'tof'`` dimension and coordinate.
+    """
+    scn.io.save_xye(filename, prepare_reduced_data(da), coord="tof")

packages/essdiffraction/tests/dream/geant4_reduction_test.py

@@ -10,6 +10,7 @@
 import scipp as sc
 import scipp.testing
 from ess import dream, powder
+from ess.dream.io import save_xye
 from ess.dream.workflows import (
     DreamGeant4MonitorHistogramWorkflow,
     DreamGeant4MonitorIntegratedWorkflow,
@@ -31,6 +32,7 @@
     LookupTableFilename,
     MonitorFilename,
     NeXusDetectorName,
+    OutFilename,
     ReducedTofCIF,
     SampleRun,
     TofMask,
@@ -289,6 +291,7 @@ def test_pipeline_save_data_to_disk(output_folder: Path):
         detector_name="mantle", run_norm=powder.RunNormalization.proton_charge
     )
 
+    wf[OutFilename] = output_folder / "dream_reduced.xye"
     wf[Filename[SampleRun]] = dream.data.simulated_diamond_sample(small=False)
     wf[Filename[VanadiumRun]] = dream.data.simulated_vanadium_sample(small=False)
     wf[Filename[EmptyCanRun]] = dream.data.simulated_empty_can(small=False)
@@ -302,6 +305,8 @@ def test_pipeline_save_data_to_disk(output_folder: Path):
     """
     result.save(output_folder / "dream_reduced.cif")
 
+    wf.bind_and_call(save_xye)
+
 
 def _assert_contains_source_info(cif_content: str) -> None:
     assert 'diffrn_source.beamline DREAM' in cif_content