generalize toListImpl to support conversions into lists and sequences

core/api/core.api

@@ -9808,8 +9808,8 @@ public final class org/jetbrains/kotlinx/dataframe/impl/api/ToDataFrameKt {
 	public static final fun createDataFrameImpl (Ljava/lang/Iterable;Lkotlin/reflect/KClass;Lkotlin/jvm/functions/Function1;)Lorg/jetbrains/kotlinx/dataframe/DataFrame;
 }
 
-public final class org/jetbrains/kotlinx/dataframe/impl/api/ToListKt {
-	public static final fun toListImpl (Lorg/jetbrains/kotlinx/dataframe/DataFrame;Lkotlin/reflect/KType;)Ljava/util/List;
+public final class org/jetbrains/kotlinx/dataframe/impl/api/ToSequenceKt {
+	public static final fun toSequenceImpl (Lorg/jetbrains/kotlinx/dataframe/DataFrame;Lkotlin/reflect/KType;)Ljava/lang/Iterable;
 }
 
 public final class org/jetbrains/kotlinx/dataframe/impl/api/UpdateKt {

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/toList.kt

@@ -2,13 +2,13 @@ package org.jetbrains.kotlinx.dataframe.api
 
 import org.jetbrains.kotlinx.dataframe.AnyFrame
 import org.jetbrains.kotlinx.dataframe.DataFrame
-import org.jetbrains.kotlinx.dataframe.impl.api.toListImpl
+import org.jetbrains.kotlinx.dataframe.impl.api.toSequenceImpl
 import kotlin.reflect.typeOf
 
 // region DataFrame
 
-public inline fun <reified T> DataFrame<T>.toList(): List<T> = toListImpl(typeOf<T>()) as List<T>
+public inline fun <reified T> DataFrame<T>.toList(): List<T> = toSequenceImpl(typeOf<T>()).toList() as List<T>
 
-public inline fun <reified T> AnyFrame.toListOf(): List<T> = toListImpl(typeOf<T>()) as List<T>
+public inline fun <reified T> AnyFrame.toListOf(): List<T> = toSequenceImpl(typeOf<T>()).toList() as List<T>
 
 // endregion

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/toSequence.kt

@@ -0,0 +1,14 @@
+package org.jetbrains.kotlinx.dataframe.api
+
+import org.jetbrains.kotlinx.dataframe.AnyFrame
+import org.jetbrains.kotlinx.dataframe.DataFrame
+import org.jetbrains.kotlinx.dataframe.impl.api.toSequenceImpl
+import kotlin.reflect.typeOf
+
+// region DataFrame
+
+public inline fun <reified T> DataFrame<T>.toSequence(): Sequence<T> = toSequenceImpl(typeOf<T>()) as Sequence<T>
+
+public inline fun <reified T> AnyFrame.toSequenceOf(): Sequence<T> = toSequenceImpl(typeOf<T>()) as Sequence<T>
+
+// endregion

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/toList.kt → core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/toSequence.kt

@@ -21,7 +21,7 @@ import kotlin.reflect.full.withNullability
 import kotlin.reflect.jvm.jvmErasure
 
 @PublishedApi
-internal fun AnyFrame.toListImpl(type: KType): List<Any> {
+internal fun AnyFrame.toSequenceImpl(type: KType): Sequence<Any> {
     val clazz = type.jvmErasure
     require(clazz.isData) { "`$clazz` is not a data class. `toList` is supported only for data classes." }
 
@@ -46,15 +46,15 @@ internal fun AnyFrame.toListImpl(type: KType): List<Any> {
                     val col: AnyCol = if (it.type.jvmErasure == List::class) {
                         val elementType = it.type.arguments[0].type
                         require(elementType != null) { "FrameColumn can not be converted to type `List<*>`" }
-                        column.asAnyFrameColumn().map { it.toListImpl(elementType) }
+                        column.asAnyFrameColumn().map { it.toSequenceImpl(elementType).toList() }
                     } else {
                         error("FrameColumn can not be converted to type `${it.type}`")
                     }
                     col
                 }
 
                 ColumnKind.Group -> {
-                    DataColumn.createValueColumn(column.name(), column.asColumnGroup().toListImpl(it.type))
+                    DataColumn.createValueColumn(column.name(), column.asColumnGroup().toSequenceImpl(it.type).toList())
                 }
 
                 ColumnKind.Value -> {
@@ -74,7 +74,7 @@ internal fun AnyFrame.toListImpl(type: KType): List<Any> {
         convertedColumn
     }
 
-    return rows().map { row ->
+    return rows().asSequence().map { row ->
         val parameters = convertedColumns
             .map { row[it] }
             .toTypedArray()

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/toList.kt

@@ -2,13 +2,13 @@ package org.jetbrains.kotlinx.dataframe.api
 
 import org.jetbrains.kotlinx.dataframe.AnyFrame
 import org.jetbrains.kotlinx.dataframe.DataFrame
-import org.jetbrains.kotlinx.dataframe.impl.api.toListImpl
+import org.jetbrains.kotlinx.dataframe.impl.api.toSequenceImpl
 import kotlin.reflect.typeOf
 
 // region DataFrame
 
-public inline fun <reified T> DataFrame<T>.toList(): List<T> = toListImpl(typeOf<T>()) as List<T>
+public inline fun <reified T> DataFrame<T>.toList(): List<T> = toSequenceImpl(typeOf<T>()).toList() as List<T>
 
-public inline fun <reified T> AnyFrame.toListOf(): List<T> = toListImpl(typeOf<T>()) as List<T>
+public inline fun <reified T> AnyFrame.toListOf(): List<T> = toSequenceImpl(typeOf<T>()).toList() as List<T>
 
 // endregion

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/toSequence.kt

@@ -0,0 +1,14 @@
+package org.jetbrains.kotlinx.dataframe.api
+
+import org.jetbrains.kotlinx.dataframe.AnyFrame
+import org.jetbrains.kotlinx.dataframe.DataFrame
+import org.jetbrains.kotlinx.dataframe.impl.api.toSequenceImpl
+import kotlin.reflect.typeOf
+
+// region DataFrame
+
+public inline fun <reified T> DataFrame<T>.toSequence(): Sequence<T> = toSequenceImpl(typeOf<T>()) as Sequence<T>
+
+public inline fun <reified T> AnyFrame.toSequenceOf(): Sequence<T> = toSequenceImpl(typeOf<T>()) as Sequence<T>
+
+// endregion

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/toList.kt → core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/toSequence.kt

@@ -21,7 +21,7 @@ import kotlin.reflect.full.withNullability
 import kotlin.reflect.jvm.jvmErasure
 
 @PublishedApi
-internal fun AnyFrame.toListImpl(type: KType): List<Any> {
+internal fun AnyFrame.toSequenceImpl(type: KType): Sequence<Any> {
     val clazz = type.jvmErasure
     require(clazz.isData) { "`$clazz` is not a data class. `toList` is supported only for data classes." }
 
@@ -46,15 +46,15 @@ internal fun AnyFrame.toListImpl(type: KType): List<Any> {
                     val col: AnyCol = if (it.type.jvmErasure == List::class) {
                         val elementType = it.type.arguments[0].type
                         require(elementType != null) { "FrameColumn can not be converted to type `List<*>`" }
-                        column.asAnyFrameColumn().map { it.toListImpl(elementType) }
+                        column.asAnyFrameColumn().map { it.toSequenceImpl(elementType).toList() }
                     } else {
                         error("FrameColumn can not be converted to type `${it.type}`")
                     }
                     col
                 }
 
                 ColumnKind.Group -> {
-                    DataColumn.createValueColumn(column.name(), column.asColumnGroup().toListImpl(it.type))
+                    DataColumn.createValueColumn(column.name(), column.asColumnGroup().toSequenceImpl(it.type).toList())
                 }
 
                 ColumnKind.Value -> {
@@ -74,7 +74,7 @@ internal fun AnyFrame.toListImpl(type: KType): List<Any> {
         convertedColumn
     }
 
-    return rows().map { row ->
+    return rows().asSequence().map { row ->
         val parameters = convertedColumns
             .map { row[it] }
             .toTypedArray()

docs/StardustDocs/topics/collectionsInterop.md

@@ -82,7 +82,7 @@ for Gradle or the [Kotlin Jupyter kernel](gettingStartedJupyterNotebook.md)
 
 </tip>
 
-After your data is transformed, [`DataFrame`](DataFrame.md) instances can be exported 
+After your data is transformed, [`DataFrame`](DataFrame.md) instances can be exported eagerly
 into [`List`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-list/) of another data class using [toList](toList.md) or [toListOf](toList.md#tolistof) extensions:
 
 <!---FUN listInterop4-->
@@ -93,6 +93,17 @@ data class Output(val a: Int, val b: Int, val c: Int)
 val result = df2.toListOf<Output>()
 ```
 
+Alternatively, one can create lazy [`Sequence`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-sequence/) objects.
+This avoids holding the entire list of objects in memory as objects are created on the fly as needed.
+
+<!---FUN listInterop5-->
+
+```kotlin
+data class Output(val a: Int, val b: Int, val c: Int)
+
+val result = df2.toSequenceOf<Output>()
+```
+
 <!---END-->
 
 ### Converting columns with object instances to ColumnGroup