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### What changes were proposed in this pull request? This PR proposes to redesign pandas UDFs as described in [the proposal](https://docs.google.com/document/d/1-kV0FS_LF2zvaRh_GhkV32Uqksm_Sq8SvnBBmRyxm30/edit?usp=sharing). ```python from pyspark.sql.functions import pandas_udf import pandas as pd pandas_udf("long") def plug_one(s: pd.Series) -> pd.Series: return s + 1 spark.range(10).select(plug_one("id")).show() ``` ``` +------------+ |plug_one(id)| +------------+ | 1| | 2| | 3| | 4| | 5| | 6| | 7| | 8| | 9| | 10| +------------+ ``` Note that, this PR address one of the future improvements described [here](https://docs.google.com/document/d/1-kV0FS_LF2zvaRh_GhkV32Uqksm_Sq8SvnBBmRyxm30/edit#heading=h.h3ncjpk6ujqu), "A couple of less-intuitive pandas UDF types" (by zero323) together. In short, - Adds new way with type hints as an alternative and experimental way. ```python pandas_udf(schema='...') def func(c1: Series, c2: Series) -> DataFrame: pass ``` - Replace and/or add an alias for three types below from UDF, and make them as separate standalone APIs. So, `pandas_udf` is now consistent with regular `udf`s and other expressions. `df.mapInPandas(udf)` -replace-> `df.mapInPandas(f, schema)` `df.groupby.apply(udf)` -alias-> `df.groupby.applyInPandas(f, schema)` `df.groupby.cogroup.apply(udf)` -replace-> `df.groupby.cogroup.applyInPandas(f, schema)` *`df.groupby.apply` was added from 2.3 while the other were added in the master only. - No deprecation for the existing ways for now. ```python pandas_udf(schema='...', functionType=PandasUDFType.SCALAR) def func(c1, c2): pass ``` If users are happy with this, I plan to deprecate the existing way and declare using type hints is not experimental anymore. One design goal in this PR was that, avoid touching the internal (since we didn't deprecate the old ways for now), but supports type hints with a minimised changes only at the interface. - Once we deprecate or remove the old ways, I think it requires another refactoring for the internal in the future. At the very least, we should rename internal pandas evaluation types. - If users find this experimental type hints isn't quite helpful, we should simply revert the changes at the interface level. ### Why are the changes needed? In order to address old design issues. Please see [the proposal](https://docs.google.com/document/d/1-kV0FS_LF2zvaRh_GhkV32Uqksm_Sq8SvnBBmRyxm30/edit?usp=sharing). ### Does this PR introduce any user-facing change? For behaviour changes, No. It adds new ways to use pandas UDFs by using type hints. See below. **SCALAR**: ```python pandas_udf(schema='...') def func(c1: Series, c2: DataFrame) -> Series: pass # DataFrame represents a struct column ``` **SCALAR_ITER**: ```python pandas_udf(schema='...') def func(iter: Iterator[Tuple[Series, DataFrame, ...]]) -> Iterator[Series]: pass # Same as SCALAR but wrapped by Iterator ``` **GROUPED_AGG**: ```python pandas_udf(schema='...') def func(c1: Series, c2: DataFrame) -> int: pass # DataFrame represents a struct column ``` **GROUPED_MAP**: This was added in Spark 2.3 as of SPARK-20396. As described above, it keeps the existing behaviour. Additionally, we now have a new alias `groupby.applyInPandas` for `groupby.apply`. See the example below: ```python def func(pdf): return pdf df.groupby("...").applyInPandas(func, schema=df.schema) ``` **MAP_ITER**: this is not a pandas UDF anymore This was added in Spark 3.0 as of SPARK-28198; and this PR replaces the usages. See the example below: ```python def func(iter): for df in iter: yield df df.mapInPandas(func, df.schema) ``` **COGROUPED_MAP**: this is not a pandas UDF anymore This was added in Spark 3.0 as of SPARK-27463; and this PR replaces the usages. See the example below: ```python def asof_join(left, right): return pd.merge_asof(left, right, on="...", by="...") df1.groupby("...").cogroup(df2.groupby("...")).applyInPandas(asof_join, schema="...") ``` ### How was this patch tested? Unittests added and tested against Python 2.7, 3.6 and 3.7. Closes #27165 from HyukjinKwon/revisit-pandas. Authored-by: HyukjinKwon <gurwls223@apache.org> Signed-off-by: HyukjinKwon <gurwls223@apache.org> |
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Apache Spark
Spark is a unified analytics engine for large-scale data processing. It provides high-level APIs in Scala, Java, Python, and R, and an optimized engine that supports general computation graphs for data analysis. It also supports a rich set of higher-level tools including Spark SQL for SQL and DataFrames, MLlib for machine learning, GraphX for graph processing, and Structured Streaming for stream processing.
Online Documentation
You can find the latest Spark documentation, including a programming guide, on the project web page. This README file only contains basic setup instructions.
Building Spark
Spark is built using Apache Maven. To build Spark and its example programs, run:
./build/mvn -DskipTests clean package
(You do not need to do this if you downloaded a pre-built package.)
More detailed documentation is available from the project site, at "Building Spark".
For general development tips, including info on developing Spark using an IDE, see "Useful Developer Tools".
Interactive Scala Shell
The easiest way to start using Spark is through the Scala shell:
./bin/spark-shell
Try the following command, which should return 1,000,000,000:
scala> spark.range(1000 * 1000 * 1000).count()
Interactive Python Shell
Alternatively, if you prefer Python, you can use the Python shell:
./bin/pyspark
And run the following command, which should also return 1,000,000,000:
>>> spark.range(1000 * 1000 * 1000).count()
Example Programs
Spark also comes with several sample programs in the examples
directory.
To run one of them, use ./bin/run-example <class> [params]
. For example:
./bin/run-example SparkPi
will run the Pi example locally.
You can set the MASTER environment variable when running examples to submit
examples to a cluster. This can be a mesos:// or spark:// URL,
"yarn" to run on YARN, and "local" to run
locally with one thread, or "local[N]" to run locally with N threads. You
can also use an abbreviated class name if the class is in the examples
package. For instance:
MASTER=spark://host:7077 ./bin/run-example SparkPi
Many of the example programs print usage help if no params are given.
Running Tests
Testing first requires building Spark. Once Spark is built, tests can be run using:
./dev/run-tests
Please see the guidance on how to run tests for a module, or individual tests.
There is also a Kubernetes integration test, see resource-managers/kubernetes/integration-tests/README.md
A Note About Hadoop Versions
Spark uses the Hadoop core library to talk to HDFS and other Hadoop-supported storage systems. Because the protocols have changed in different versions of Hadoop, you must build Spark against the same version that your cluster runs.
Please refer to the build documentation at "Specifying the Hadoop Version and Enabling YARN" for detailed guidance on building for a particular distribution of Hadoop, including building for particular Hive and Hive Thriftserver distributions.
Configuration
Please refer to the Configuration Guide in the online documentation for an overview on how to configure Spark.
Contributing
Please review the Contribution to Spark guide for information on how to get started contributing to the project.