Merge pull request Kotlin#801 from Kotlin/implodeFix

Small implode fix

Author: Jolanrensen

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

@@ -30,8 +30,14 @@ internal fun <T, C> DataFrame<T>.implodeImpl(dropNA: Boolean = false, columns: C
  first = false
  value
  } else {
- null
+ // these rows will not be taken into account,
+ // but we cannot leave them empty, as `map` creates a full column
+ when (column.kind()) {
+ ColumnKind.Value -> emptyList<Any?>()
+ ColumnKind.Group -> DataFrame.empty()
+ ColumnKind.Frame -> emptyList<AnyFrame>()
+ }
  }
  }
- }[0..0]
+ }[0..0] // takes only the first row
  }.concat()

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/columns/DataColumnImpl.kt

@@ -5,6 +5,7 @@ import org.jetbrains.kotlinx.dataframe.DataColumn
 import org.jetbrains.kotlinx.dataframe.api.dataFrameOf
 import org.jetbrains.kotlinx.dataframe.impl.isArray
 import org.jetbrains.kotlinx.dataframe.impl.isPrimitiveArray
+import org.jetbrains.kotlinx.dataframe.kind
 import kotlin.reflect.KClass
 import kotlin.reflect.KType
 import kotlin.reflect.full.isSubclassOf
@@ -37,7 +38,7 @@ internal abstract class DataColumnImpl<T>(
  if (BuildConfig.DEBUG) {
  require(values.all { it matches type }) {
  val types = values.map { if (it == null) "Nothing?" else it!!::class.simpleName }.distinct()
- "Values of column '$name' have types '$types' which are not compatible given with column type '$type'"
+ "Values of $kind '$name' have types '$types' which are not compatible given with column type '$type'"
  }
  }
  }