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https://issues.apache.org/jira/browse/SPARK-22283?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16207780#comment-16207780
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Liang-Chi Hsieh commented on SPARK-22283:
-----------------------------------------
When joined result has duplicate column name, you can't select any of the
ambiguous columns by just name. Doesn't {{withColumn}} current behavior simply
follow it?
> withColumn should replace multiple instances with a single one
> --------------------------------------------------------------
>
> Key: SPARK-22283
> URL: https://issues.apache.org/jira/browse/SPARK-22283
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.2.0
> Reporter: Albert Meltzer
>
> Currently, {{withColumn}} claims to do the following: _"adding a column or
> replacing the existing column that has the same name."_
> Unfortunately, if multiple existing columns have the same name (which is a
> normal occurrence after a join), this results in multiple replaced -- and
> retained --
> columns (with the same value), and messages about an ambiguous column.
> The current implementation of {{withColumn}} contains this:
> {noformat}
> def withColumn(colName: String, col: Column): DataFrame = {
> val resolver = sparkSession.sessionState.analyzer.resolver
> val output = queryExecution.analyzed.output
> val shouldReplace = output.exists(f => resolver(f.name, colName))
> if (shouldReplace) {
> val columns = output.map { field =>
> if (resolver(field.name, colName)) {
> col.as(colName)
> } else {
> Column(field)
> }
> }
> select(columns : _*)
> } else {
> select(Column("*"), col.as(colName))
> }
> }
> {noformat}
> Instead, suggest something like this (which replaces all matching fields with
> a single instance of the new one):
> {noformat}
> def withColumn(colName: String, col: Column): DataFrame = {
> val resolver = sparkSession.sessionState.analyzer.resolver
> val output = queryExecution.analyzed.output
> val existing = output.filterNot(f => resolver(f.name, colName)).map(new
> Column(_))
> select(existing :+ col.as(colName): _*)
> }
> {noformat}
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