DM-43176: Add deblender metric to count children with no flux after re-distribution

python/lsst/analysis/tools/actions/vector/selectors.py

@@ -545,6 +545,32 @@ def setDefaults(self):
         self.selectWhenTrue = ["detect_isPatchInner"]
 
 
+class ChildObjectSelector(RangeSelector):
+    """Select only children from deblended parents"""
+
+    vectorKey = Field[str](doc="Key to select from data", default="parentSourceId")
+
+    def getInputSchema(self) -> KeyedDataSchema:
+        yield self.vectorKey, Vector
+
+    def __call__(self, data: KeyedData, **kwargs) -> Vector:
+        """Return a mask of rows with values within the specified range.
+
+        Parameters
+        ----------
+        data : `KeyedData`
+
+        Returns
+        -------
+        result : `Vector`
+            A mask of the rows with values within the specified range.
+        """
+        values = cast(Vector, data[self.vectorKey])
+        mask = values > 0
+
+        return cast(Vector, mask)
+
+
 class MagSelector(SelectorBase):
     """Selects points that have minMag < mag (AB) < maxMag.
 

python/lsst/analysis/tools/atools/deblenderMetric.py

@@ -23,7 +23,12 @@
 __all__ = ("ParentDeblenderMetrics", "SkippedDeblenderMetrics", "BlendMetrics", "IsolatedDeblenderMetrics")
 
 from ..actions.scalar.scalarActions import CountAction, MeanAction, SumAction
-from ..actions.vector.selectors import FlagSelector, ParentObjectSelector, ThresholdSelector
+from ..actions.vector.selectors import (
+    ChildObjectSelector,
+    FlagSelector,
+    ParentObjectSelector,
+    ThresholdSelector,
+)
 from ..interfaces import AnalysisTool
 
 
@@ -140,3 +145,18 @@ def setDefaults(self):
             "meanIsolatedIterations": "",
             "meanIsolatedLogL": "",
         }
+
+
+class ChildDeblenderMetrics(AnalysisTool):
+    """Calculate metrics based on the performance of the deblender for
+    single sources.
+    """
+
+    def setDefaults(self):
+        super().setDefaults()
+        self.prep.selectors.childSelector = ChildObjectSelector()
+        self.process.calculateActions.zeroFlux = SumAction(vectorKey="deblend_zeroFlux")
+
+        self.produce.metric.units = {
+            "zeroFlux": "",
+        }