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From "Shivaram Venkataraman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-10894) Add 'drop' support for DataFrame's subset function
Date Thu, 01 Oct 2015 16:25:26 GMT

    [ https://issues.apache.org/jira/browse/SPARK-10894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940037#comment-14940037
] 

Shivaram Venkataraman commented on SPARK-10894:
-----------------------------------------------

I'm not sure this is a very useful feature as the `Column` data structure in SparkR does not
have any functions supported on it and is a pointer that can be passed around.  Are there
any use cases that this helps in SparkR that you see ? 

> Add 'drop' support for DataFrame's subset function
> --------------------------------------------------
>
>                 Key: SPARK-10894
>                 URL: https://issues.apache.org/jira/browse/SPARK-10894
>             Project: Spark
>          Issue Type: Improvement
>          Components: SparkR
>            Reporter: Weiqiang Zhuang
>
> SparkR DataFrame can be subset to get one or more columns of the dataset. The current
'[' implementation does not support 'drop' when is asked for just one column. This is not
consistent with the R syntax:
> x[i, j, ... , drop = TRUE]
> # in R, when drop is FALSE, remain as data.frame
> > class(iris[, "Sepal.Width", drop=F])
> [1] "data.frame"
> # when drop is TRUE (default), drop to be a vector
> > class(iris[, "Sepal.Width", drop=T])
> [1] "numeric"
> > class(iris[,"Sepal.Width"])
> [1] "numeric"
> > df <- createDataFrame(sqlContext, iris)
> # in SparkR, 'drop' argument has no impact
> > class(df[,"Sepal_Width", drop=F])
> [1] "DataFrame"
> attr(,"package")
> [1] "SparkR"
> # should have dropped to be a Column class instead
> > class(df[,"Sepal_Width", drop=T])
> [1] "DataFrame"
> attr(,"package")
> [1] "SparkR"
> > class(df[,"Sepal_Width"])
> [1] "DataFrame"
> attr(,"package")
> [1] "SparkR"
> We should add the 'drop' support.



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