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https://issues.apache.org/jira/browse/SPARK-21190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16151376#comment-16151376
]
Leif Walsh commented on SPARK-21190:
------------------------------------
Yep, that's totally a thing:
{noformat}In [1]: import pandas as pd
In [2]: pd.DataFrame(index=list(range(100)))
Out[2]:
Empty DataFrame
Columns: []
Index: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
[100 rows x 0 columns]
In [3]: df = Out[2]
In [4]: pd.Series(data=1, index=df.index)
Out[4]:
0 1
1 1
2 1
3 1
4 1
5 1
6 1
7 1
8 1
9 1
10 1
11 1
12 1
13 1
14 1
15 1
16 1
17 1
18 1
19 1
20 1
21 1
22 1
23 1
24 1
25 1
26 1
27 1
28 1
29 1
..
70 1
71 1
72 1
73 1
74 1
75 1
76 1
77 1
78 1
79 1
80 1
81 1
82 1
83 1
84 1
85 1
86 1
87 1
88 1
89 1
90 1
91 1
92 1
93 1
94 1
95 1
96 1
97 1
98 1
99 1
Length: 100, dtype: int64
{noformat}
So, how about:
{noformat}
@pandas_udf(LongType())
def f0(df):
return pd.Series(data=1, index=df.index)
df.select(f0())
{noformat}
> SPIP: Vectorized UDFs in Python
> -------------------------------
>
> Key: SPARK-21190
> URL: https://issues.apache.org/jira/browse/SPARK-21190
> Project: Spark
> Issue Type: New Feature
> Components: PySpark, SQL
> Affects Versions: 2.2.0
> Reporter: Reynold Xin
> Assignee: Reynold Xin
> Labels: SPIP
> Attachments: SPIPVectorizedUDFsforPython (1).pdf
>
>
> *Background and Motivation*
> Python is one of the most popular programming languages among Spark users.
> Spark currently exposes a row-at-a-time interface for defining and executing
> user-defined functions (UDFs). This introduces high overhead in serialization
> and deserialization, and also makes it difficult to leverage Python libraries
> (e.g. numpy, Pandas) that are written in native code.
>
> This proposal advocates introducing new APIs to support vectorized UDFs in
> Python, in which a block of data is transferred over to Python in some
> columnar format for execution.
>
>
> *Target Personas*
> Data scientists, data engineers, library developers.
>
> *Goals*
> - Support vectorized UDFs that apply on chunks of the data frame
> - Low system overhead: Substantially reduce serialization and deserialization
> overhead when compared with row-at-a-time interface
> - UDF performance: Enable users to leverage native libraries in Python (e.g.
> numpy, Pandas) for data manipulation in these UDFs
>
> *Non-Goals*
> The following are explicitly out of scope for the current SPIP, and should be
> done in future SPIPs. Nonetheless, it would be good to consider these future
> use cases during API design, so we can achieve some consistency when rolling
> out new APIs.
>
> - Define block oriented UDFs in other languages (that are not Python).
> - Define aggregate UDFs
> - Tight integration with machine learning frameworks
>
> *Proposed API Changes*
> The following sketches some possibilities. I haven’t spent a lot of time
> thinking about the API (wrote it down in 5 mins) and I am not attached to
> this design at all. The main purpose of the SPIP is to get feedback on use
> cases and see how they can impact API design.
>
> A few things to consider are:
>
> 1. Python is dynamically typed, whereas DataFrames/SQL requires static,
> analysis time typing. This means users would need to specify the return type
> of their UDFs.
>
> 2. Ratio of input rows to output rows. We propose initially we require number
> of output rows to be the same as the number of input rows. In the future, we
> can consider relaxing this constraint with support for vectorized aggregate
> UDFs.
> 3. How do we handle null values, since Pandas doesn't have the concept of
> nulls?
>
> Proposed API sketch (using examples):
>
> Use case 1. A function that defines all the columns of a DataFrame (similar
> to a “map” function):
>
> {code}
> @spark_udf(some way to describe the return schema)
> def my_func_on_entire_df(input):
> """ Some user-defined function.
>
> :param input: A Pandas DataFrame with two columns, a and b.
> :return: :class: A Pandas data frame.
> """
> input[c] = input[a] + input[b]
> Input[d] = input[a] - input[b]
> return input
>
> spark.range(1000).selectExpr("id a", "id / 2 b")
> .mapBatches(my_func_on_entire_df)
> {code}
>
> Use case 2. A function that defines only one column (similar to existing
> UDFs):
>
> {code}
> @spark_udf(some way to describe the return schema)
> def my_func_that_returns_one_column(input):
> """ Some user-defined function.
>
> :param input: A Pandas DataFrame with two columns, a and b.
> :return: :class: A numpy array
> """
> return input[a] + input[b]
>
> my_func = udf(my_func_that_returns_one_column)
>
> df = spark.range(1000).selectExpr("id a", "id / 2 b")
> df.withColumn("c", my_func(df.a, df.b))
> {code}
>
>
>
> *Optional Design Sketch*
> I’m more concerned about getting proper feedback for API design. The
> implementation should be pretty straightforward and is not a huge concern at
> this point. We can leverage the same implementation for faster toPandas
> (using Arrow).
>
>
> *Optional Rejected Designs*
> See above.
>
>
>
>
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