HyukjinKwon commented on a change in pull request #32926:
URL: https://github.com/apache/spark/pull/32926#discussion_r652406643
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File path: python/docs/source/development/ps_design.rst
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@@ -1,85 +0,0 @@
-=================
-Design Principles
-=================
-
-.. currentmodule:: pyspark.pandas
-
-This section outlines design principles guiding the pandas API on Spark.
-
-Be Pythonic
------------
-
-Pandas API on Spark targets Python data scientists. We want to stick to the
convention that users are already familiar with as much as possible. Here are
some examples:
-
-- Function names and parameters use snake_case, rather than CamelCase. This is
different from PySpark's design. For example, pandas API on Spark has
`to_pandas()`, whereas PySpark has `toPandas()` for converting a DataFrame into
a pandas DataFrame. In limited cases, to maintain compatibility with Spark, we
also provide Spark's variant as an alias.
-
-- Pandas API on Spark respects to the largest extent the conventions of the
Python numerical ecosystem, and allows the use of NumPy types, etc. that can be
supported by Spark.
-
-- pandas-on-Spark docs' style and infrastructure simply follow rest of the
PyData projects'.
-
-Unify small data (pandas) API and big data (Spark) API, but pandas first
-------------------------------------------------------------------------
-
-The pandas-on-Spark DataFrame is meant to provide the best of pandas and Spark
under a single API, with easy and clear conversions between each API when
necessary. When Spark and pandas have similar APIs with subtle differences, the
principle is to honor the contract of the pandas API first.
-
-There are different classes of functions:
-
- 1. Functions that are found in both Spark and pandas under the same name
(`count`, `dtypes`, `head`). The return value is the same as the return type in
pandas (and not Spark's).
-
- 2. Functions that are found in Spark but that have a clear equivalent in
pandas, e.g. `alias` and `rename`. These functions will be implemented as the
alias of the pandas function, but should be marked that they are aliases of the
same functions. They are provided so that existing users of PySpark can get the
benefits of pandas API on Spark without having to adapt their code.
-
- 3. Functions that are only found in pandas. When these functions are
appropriate for distributed datasets, they should become available in pandas
API on Spark.
-
- 4. Functions that are only found in Spark that are essential to controlling
the distributed nature of the computations, e.g. `cache`. These functions
should be available in pandas API on Spark.
-
-We are still debating whether data transformation functions only available in
Spark should be added to pandas API on Spark, e.g. `select`. We would love to
hear your feedback on that.
-
-Return pandas-on-Spark data structure for big data, and pandas data structure
for small data
---------------------------------------------------------------------------------------------
-
-Often developers face the question whether a particular function should return
a pandas-on-Spark DataFrame/Series, or a pandas DataFrame/Series. The principle
is: if the returned object can be large, use a pandas-on-Spark
DataFrame/Series. If the data is bound to be small, use a pandas
DataFrame/Series. For example, `DataFrame.dtypes` return a pandas Series,
because the number of columns in a DataFrame is bounded and small, whereas
`DataFrame.head()` or `Series.unique()` returns a pandas-on-Spark
DataFrame/Series, because the resulting object can be large.
-
-Provide discoverable APIs for common data science tasks
Review comment:
Moved and merged
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