diff --git a/core/src/main/kotlin/ch/kleis/lcaac/core/datasource/DataSourceOperationsBase.kt b/core/src/main/kotlin/ch/kleis/lcaac/core/datasource/DataSourceOperationsBase.kt
index 6496d788..0c217106 100644
--- a/core/src/main/kotlin/ch/kleis/lcaac/core/datasource/DataSourceOperationsBase.kt
+++ b/core/src/main/kotlin/ch/kleis/lcaac/core/datasource/DataSourceOperationsBase.kt
@@ -21,12 +21,6 @@ open class DataSourceOperationsBase<Q>(
         val description = DataSourceDescription(source.location, source.schema)
         val records = load(description)
         val filter = source.filter
-        val reducer = DataExpressionReducer(
-            dataRegister = Prelude.units(),
-            dataSourceRegister = DataSourceRegister.empty(),
-            ops = ops,
-            sourceOps = this,
-        )
         return records
             .filter { record ->
                 filter.entries.all {
@@ -40,10 +34,6 @@ open class DataSourceOperationsBase<Q>(
                         actual == expected
                     } else throw EvaluatorException("invalid matching condition $it")
                 }
-            }.map { record ->
-                ERecord(
-                    record.entries.mapValues { reducer.reduce(it.value) }
-                )
             }
     }
 
diff --git a/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducer.kt b/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducer.kt
index 275b0e15..f6b616f0 100644
--- a/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducer.kt
+++ b/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducer.kt
@@ -50,7 +50,7 @@ class DataExpressionReducer<Q>(
 
     private fun reduceFirstRecordOf(expression: EFirstRecordOf<Q>): DataExpression<Q> {
         val dataSource = evalDataSource(expression.dataSource)
-        return sourceOps.getFirst(dataSource)
+        return reduceMap(sourceOps.getFirst(dataSource))
     }
 
     fun reduceDataSource(expression: DataSourceExpression<Q>, filter: Map<String, DataExpression<Q>> = emptyMap()): EDataSource<Q> {
diff --git a/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/LcaExpressionReducer.kt b/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/LcaExpressionReducer.kt
index d556db6e..4eb5a067 100644
--- a/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/LcaExpressionReducer.kt
+++ b/core/src/main/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/LcaExpressionReducer.kt
@@ -85,6 +85,7 @@ class LcaExpressionReducer<Q>(
             is EBlockForEach -> {
                 val ds = dataExpressionReducer.evalDataSource(expression.dataSource)
                 sourceOps.readAll(ds)
+                    .map { dataExpressionReducer.reduce(it) }
                     .flatMap { record ->
                         val reducer = push(mapOf(
                             DataKey(expression.rowRef) to record
@@ -110,6 +111,7 @@ class LcaExpressionReducer<Q>(
             is EBlockForEach -> {
                 val ds = dataExpressionReducer.evalDataSource(expression.dataSource)
                 sourceOps.readAll(ds)
+                    .map { dataExpressionReducer.reduce(it) }
                     .flatMap { record ->
                         val reducer = push(mapOf(
                             DataKey(expression.rowRef) to record
@@ -135,6 +137,7 @@ class LcaExpressionReducer<Q>(
             is EBlockForEach -> {
                 val ds = dataExpressionReducer.evalDataSource(expression.dataSource)
                 sourceOps.readAll(ds)
+                    .map { dataExpressionReducer.reduce(it) }
                     .flatMap { record ->
                         val reducer = push(mapOf(
                             DataKey(expression.rowRef) to record
diff --git a/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducerTest.kt b/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducerTest.kt
index 4cd540a9..37c35166 100644
--- a/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducerTest.kt
+++ b/core/src/test/kotlin/ch/kleis/lcaac/core/lang/evaluator/reducer/DataExpressionReducerTest.kt
@@ -255,7 +255,7 @@ class DataExpressionReducerTest {
                 "mass" to QuantityFixture.oneKilogram
             )
         )
-        val record = EFirstRecordOf<BasicNumber>(EDataSourceRef("source"))
+        val firstRecordOf = EFirstRecordOf<BasicNumber>(EDataSourceRef("source"))
         val reducer = DataExpressionReducer(
             DataRegister.empty(),
             DataSourceRegister.from(mapOf(
@@ -264,12 +264,16 @@ class DataExpressionReducerTest {
             ops,
             sourceOps,
         )
-        val expected = mockk<ERecord<BasicNumber>>()
+        val expected = ERecord(
+            mapOf(
+                "mass" to QuantityFixture.twoKilograms
+            )
+        )
         val dataSourceValue = with(ToValue(ops)) { dataSource.toValue() }
         every { sourceOps.getFirst(dataSourceValue) } returns expected
 
         // when
-        val actual = reducer.reduce(record)
+        val actual = reducer.reduce(firstRecordOf)
 
         // then
         assertEquals(expected, actual)