[jira] [Commented] (SPARK-24835) col function ignores drop

["Liang-Chi Hsieh (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-24835?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16547123#comment-16547123 ] 

Liang-Chi Hsieh commented on SPARK-24835:
-----------------------------------------

`drop` actually does to add a projection on top of original dataset. So the following query works:

{code}
df2 = df.drop('c')
df2.where(df['c'] < 6).show()
{code}

It can be seen as a query (in Scala) like:

{code}
val df = Seq(("test1", 0), ("test2", 1)).toDF("name", "id")
val filter1 = df.select(df("name")).filter(df("id") === 0)
{code}

This is a valid query.

Regarding the query can't be run:

{code}
df = df.drop('c')
df.where(df['c'] < 6).show()
{code}

Because you want to resolve column {{c}} on the top of updated {{df}} which have output {{[a, b]}} now, you can't successfully resolve this column.



> col function ignores drop
> -------------------------
>
>                 Key: SPARK-24835
>                 URL: https://issues.apache.org/jira/browse/SPARK-24835
>             Project: Spark
>          Issue Type: Bug
>          Components: PySpark
>    Affects Versions: 2.3.0
>         Environment: Spark 2.3.0
> Python 3.5.3
>            Reporter: Michael Souder
>            Priority: Minor
>
> Not sure if this is a bug or user error, but I've noticed that accessing columns with the col function ignores a previous call to drop.
> {code}
> import pyspark.sql.functions as F
> df = spark.createDataFrame([(1,3,5), (2, None, 7), (0, 3, 2)], ['a', 'b', 'c'])
> df.show()
> +---+----+---+
> |  a|   b|  c|
> +---+----+---+
> |  1|   3|  5|
> |  2|null|  7|
> |  0|   3|  2|
> +---+----+---+
> df = df.drop('c')
> # the col function is able to see the 'c' column even though it has been dropped
> df.where(F.col('c') < 6).show()
> +---+---+
> |  a|  b|
> +---+---+
> |  1|  3|
> |  0|  3|
> +---+---+
> # trying the same with brackets on the data frame fails with the expected error
> df.where(df['c'] < 6).show()
> Py4JJavaError: An error occurred while calling o36909.apply.
> : org.apache.spark.sql.AnalysisException: Cannot resolve column name "c" among (a, b);{code}



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