[SPARK-15672][R][DOC] R programming guide update

[vectorijk]

What changes were proposed in this pull request?

Guide for

• UDFs with dapply, dapplyCollect
• spark.lapply for running parallel R functions

How was this patch tested?

build locally

[vectorijk]

cc @jkbradley@shivaram

[SparkQA]

Test build #60485 has finished for PR 13660 at commit 2611549.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[shivaram]

It will be good to add an introduction here that there are two kinds of user-defined functions we support in SparkR. Something like

In SparkR we support two kinds for user-defined functions
1. Run a given function on a large dataset using dapply. 2. Run many functions in parallel using spark.lapply. 

[shivaram]

Thanks @vectorijk - I left some comments inline.

cc @felixcheung

[felixcheung]

perhaps explain why the schema needs to be passed here?

[jkbradley]

Ping @vectorijk

[vectorijk]

@jkbradley@shivaram@felixcheung addressed comments.

[SparkQA]

Test build #60788 has finished for PR 13660 at commit 920c975.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #60787 has finished for PR 13660 at commit 063bc8e.

• This patch fails Spark unit tests.
• This patch does not merge cleanly.
• This patch adds no public classes.

[vectorijk]

Jenkins test this again.

[felixcheung]

great! please see pending PR #13752 on removing sc parameter from spark.lapply

[NarineK]

Hi @vectorijk , @felixcheung , @sun-rui , @shivaram
As I was looking at the dapply's documentation generated in R I've noticed that there is some duplicated information. I'm not sure if this is the right place to ask about it, but I thought you might have seen it.
In I help I see the following:

Arguments
x A SparkDataFrame
func A function to be applied to each partition of the SparkDataFrame. func should have only one parameter, to which a data.frame corresponds to each partition will be passed. The output of func should be a data.frame.
schema The schema of the resulting SparkDataFrame after the function is applied. It must match the output of func.
x A SparkDataFrame
func A function to be applied to each partition of the SparkDataFrame. func should have only one parameter, to which a data.frame corresponds to each partition will be passed. The output of func should be a data.frame.
See Also
Other SparkDataFrame functions: SparkDataFrame-class, [[, agg, arrange, as.data.frame, attach, cache, collect, colnames, coltypes, columns, count, createOrReplaceTempView, describe, dim, distinct, dropDuplicates, dropna, drop, dtypes, except, explain, filter, first, gapplyCollect, gapply, group_by, head, histogram, insertInto, intersect, isLocal, join, limit, merge, mutate, ncol, persist, printSchema, rename, repartition, sample, saveAsTable, selectExpr, select, showDF, show, str, take, unionAll, unpersist, withColumn, with, write.df, write.jdbc, write.json, write.parquet, write.text
Other SparkDataFrame functions: SparkDataFrame-class, [[, agg, arrange, as.data.frame, attach, cache, collect, colnames, coltypes, columns, count, createOrReplaceTempView, describe, dim, distinct, dropDuplicates, dropna, drop, dtypes, except, explain, filter, first, gapplyCollect, gapply, group_by, head, histogram, insertInto, intersect, isLocal, join, limit, merge, mutate, ncol, persist, printSchema, rename, repartition, sample, saveAsTable, selectExpr, select, showDF, show, str, take, unionAll, unpersist, withColumn, with, write.df, write.jdbc, write.json, write.parquet, write.text

Is this on purpose ?

[felixcheung]

@NarineK That is sort of unrelated to this PR since this PR is about the programming guide?

But in short, this happens because in the R code both dapply and dapplyCollect has the @rdname tag to "dapply". I'm not sure if we need to do that. But the first copy of "x ..." and "func ..." is from "dapply" and the second is from "dapplyCollect".

[shivaram]

Yeah we can remove the duplication by having separate rd files or by just removing documentation for the overlapping arguments (I think in this case x and func are the same for dapply and dapplyCollect).

@NarineK feel free to open a separate JIRA/PR for this

[SparkQA]

Test build #60863 has finished for PR 13660 at commit 3f2aea9.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[shivaram]

I think its good to say a couple of things here. First that we don't require any schema to be passed in to dapplyCollect (unlike dapply). The other thing is that its good to remind users that this should be used only if the output of the UDF run on all the partitions can fit in driver memory.

[SparkQA]

Test build #60918 has finished for PR 13660 at commit ae26233.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[sun-rui]

Can you add documentation for gapply() and gapplyCollect() together here? or @NarineK will do in another PR?

[sun-rui]

several kinds of?