awdavidson commented on code in PR #36150: URL: https://github.com/apache/spark/pull/36150#discussion_r858673239
########## sql/core/src/main/scala/org/apache/spark/sql/Melt.scala: ########## @@ -0,0 +1,113 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.spark.sql + +import org.apache.spark.sql.catalyst.expressions.{AttributeReference, Expression, Literal} +import org.apache.spark.sql.catalyst.expressions.objects.AssertNotNull +import org.apache.spark.sql.catalyst.plans.logical.Expand +import org.apache.spark.sql.functions.col +import org.apache.spark.sql.types.StringType + +private[sql] object Melt { + def of[_](ds: Dataset[_], + ids: Seq[String], + values: Seq[String] = Seq.empty, + dropNulls: Boolean = false, + variableColumnName: String = "variable", + valueColumnName: String = "value"): DataFrame = { + // if no values given, all non-id columns are melted + val valueNames = if (values.isEmpty) { + ds.columns.diff(ids).toSeq + } else { + values + } + + // resolve given column names + val resolver = ds.sparkSession.sessionState.analyzer.resolver + val resolvedIds = ids.map(c => + (c, ds.queryExecution.analyzed.resolveQuoted(c, resolver).map(_.toAttribute)) + ).toMap + val resolvedValues = valueNames.map(c => + (c, ds.queryExecution.analyzed.resolveQuoted(c, resolver).map(_.toAttribute)) + ).toMap + + // all given ids and values should exist in ds + val unresolvedColumns = (resolvedIds ++ resolvedValues).filter(_._2.isEmpty).keys + if (unresolvedColumns.nonEmpty) { + throw new IllegalArgumentException( + s"Unknown columns: ${unresolvedColumns.mkString(", ")}, " + + s"dataset has: ${ds.columns.mkString(", ")}" + ) + } + + // if there are no values given and no non-id columns exist, we cannot melt + if (valueNames.isEmpty) { + throw new IllegalArgumentException("The dataset has no non-id columns to melt") + } + + // all melted values have to have the same type + val valueTypes = resolvedValues.filter(_._2.isDefined).values.map(_.get.dataType).toSet + if (valueTypes.size > 1) { + throw new IllegalArgumentException(f"All values must be of same types, " + + f"found: ${valueTypes.toSeq.map(_.toString).sorted.mkString(", ")}") + } + val valueType = valueTypes.head + + // resolve ids + val idAttrs = resolvedIds.filter(_._2.isDefined).values.map(_.get.toAttribute).toSeq + val idNames = idAttrs.map(_.name) + if (idNames.contains(variableColumnName)) { + throw new IllegalArgumentException(f"Column name for variable column ($variableColumnName) " + + f"must not exist among id columns: ${idNames.mkString(", ")}") + } + if (idNames.contains(valueColumnName)) { + throw new IllegalArgumentException(f"Column name for value column ($valueColumnName) " + + f"must not exist among id columns: ${idNames.mkString(", ")}") + } + + // construct output attributes + val variableAttr = AttributeReference(variableColumnName, StringType, nullable = false)() + val valueAttr = AttributeReference(valueColumnName, valueType, nullable = true)() + val output = idAttrs ++ Seq(variableAttr, valueAttr) + + // construct melt expressions for Expand + val valueAttrs = resolvedValues.filter(_._2.isDefined).values.map(_.get.toAttribute).toSeq Review Comment: nit: we could do the `resolvedValues.filter(_._2.isDefined)` once above and reuse here. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
