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https://issues.apache.org/jira/browse/SPARK-10894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14941375#comment-14941375
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Weiqiang Zhuang commented on SPARK-10894:
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Guess it will be difficult to explain this to existing customers. BTW, dplyr
references the column by its name instead of '$' function. We should be also
able to implement that with substitute, eval and parse R functions. In fact, I
just looked at this JIRA https://issues.apache.org/jira/browse/SPARK-7499,
which looks like the better approach. But maybe there are other aspects of the
original design that this can't be done.
> 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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