Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
HyukjinKwon closed pull request #45363: [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation URL: https://github.com/apache/spark/pull/45363 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org - To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
HyukjinKwon commented on PR #45363: URL: https://github.com/apache/spark/pull/45363#issuecomment-1977745985 Merged to master. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org - To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
nchammas commented on PR #45363: URL: https://github.com/apache/spark/pull/45363#issuecomment-1976753715 I've updated the screenshots in the PR description to reflect the latest changes. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org - To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
HyukjinKwon commented on code in PR #45363: URL: https://github.com/apache/spark/pull/45363#discussion_r1510598001 ## python/pyspark/sql/group.py: ## @@ -450,6 +446,10 @@ def pivot(self, pivot_col: str, values: Optional[List["LiteralType"]] = None) -> values : list, optional List of values that will be translated to columns in the output DataFrame. +.. note:: If ``values`` is not provided, Spark will **eagerly** compute the distinct Review Comment: this too. I would just put it up in the doctest (like `DataFrameReader.csv`) -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org - To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
nchammas commented on code in PR #45363:
URL: https://github.com/apache/spark/pull/45363#discussion_r151059
##
connector/connect/client/jvm/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala:
##
@@ -259,18 +259,19 @@ class RelationalGroupedDataset private[sql] (
/**
* Pivots a column of the current `DataFrame` and performs the specified
aggregation.
*
- * There are two versions of `pivot` function: one that requires the caller
to specify the list
- * of distinct values to pivot on, and one that does not. The latter is more
concise but less
- * efficient, because Spark needs to first compute the list of distinct
values internally.
- *
* {{{
* // Compute the sum of earnings for each year by course with each course
as a separate column
- * df.groupBy("year").pivot("course", Seq("dotNET",
"Java")).sum("earnings")
- *
- * // Or without specifying column values (less efficient)
* df.groupBy("year").pivot("course").sum("earnings")
* }}}
*
+ * @note
Review Comment:
I trimmed the note a bit. Is that better?
I also took a look at the CSV reader method:
https://github.com/apache/spark/blob/a1b0da200b271214e9d6b3170308509d7d514c7f/sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala#L530-L532
It's pretty similar to what I'm proposing here.
I believe it's more important to highlight the eager computation here since
`pivot` is a transformation and, unlike with reader methods, users are probably
not expecting expensive computations to be triggered. But I agree, we don't
want to make it sound like there's something _wrong_ with not specifying pivot
values.
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Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
HyukjinKwon commented on code in PR #45363:
URL: https://github.com/apache/spark/pull/45363#discussion_r1510453526
##
connector/connect/client/jvm/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala:
##
@@ -259,18 +259,19 @@ class RelationalGroupedDataset private[sql] (
/**
* Pivots a column of the current `DataFrame` and performs the specified
aggregation.
*
- * There are two versions of `pivot` function: one that requires the caller
to specify the list
- * of distinct values to pivot on, and one that does not. The latter is more
concise but less
- * efficient, because Spark needs to first compute the list of distinct
values internally.
- *
* {{{
* // Compute the sum of earnings for each year by course with each course
as a separate column
- * df.groupBy("year").pivot("course", Seq("dotNET",
"Java")).sum("earnings")
- *
- * // Or without specifying column values (less efficient)
* df.groupBy("year").pivot("course").sum("earnings")
* }}}
*
+ * @note
Review Comment:
I wonder if we can just make it a bit shorter, and put it into the main doc
instead of the separate note. I don't want to scare users about this .. e.g.,
`DataFrameReader.csv` about schema inference.
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Re: [PR] [SPARK-47252][DOCS] Clarify that pivot may trigger an eager computation [spark]
nchammas commented on code in PR #45363:
URL: https://github.com/apache/spark/pull/45363#discussion_r1510094130
##
sql/core/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala:
##
@@ -324,18 +324,18 @@ class RelationalGroupedDataset protected[sql](
/**
* Pivots a column of the current `DataFrame` and performs the specified
aggregation.
*
- * There are two versions of `pivot` function: one that requires the caller
to specify the list
- * of distinct values to pivot on, and one that does not. The latter is more
concise but less
- * efficient, because Spark needs to first compute the list of distinct
values internally.
- *
* {{{
* // Compute the sum of earnings for each year by course with each course
as a separate column
- * df.groupBy("year").pivot("course", Seq("dotNET",
"Java")).sum("earnings")
- *
- * // Or without specifying column values (less efficient)
* df.groupBy("year").pivot("course").sum("earnings")
* }}}
*
+ * @note Spark will '''eagerly''' compute the distinct values in
`pivotColumn` so it can determine
+ *the resulting schema of the transformation. Depending on the size and
complexity of your
+ *data, this may take some time. In other words, though the pivot
transformation is lazy like
+ *most DataFrame transformations, computing the distinct pivot values is
not. To avoid any
+ *eager computations, provide an explicit list of values via
+ *`pivot(pivotColumn: String, values: Seq[Any])`.
Review Comment:
I probably spent about an hour trying to get this to work as a proper link
via `[[pivot(...]]`, per [the scaladoc docs on ambiguous links][1], but I could
not get it to work.
[1]:
https://docs.scala-lang.org/overviews/scaladoc/for-library-authors.html#resolving-ambiguous-links-within-scaladoc-comments
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