[jira] [Commented] (ARROW-1964) [Python] Expose Builder classes

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-1964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16447201#comment-16447201 ] 

ASF GitHub Bot commented on ARROW-1964:
---------------------------------------

dsimmie opened a new pull request #1930: ARROW-1964: [Python ] Exposed StringBuilder to Cython
URL: https://github.com/apache/arrow/pull/1930
 
 
   * Partial implementation of ARROW-1964
   * Only implements StringBuilder not the other builders, notably the DictionaryBuilder mentioned in issue 1964

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> [Python] Expose Builder classes
> -------------------------------
>
>                 Key: ARROW-1964
>                 URL: https://issues.apache.org/jira/browse/ARROW-1964
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: Python
>            Reporter: Uwe L. Korn
>            Priority: Major
>              Labels: beginner, pull-request-available
>             Fix For: 1.0.0
>
>
> Having the builder classes available from Python would be very helpful. Currently a construction of an Arrow array always need to have a Python list or numpy array as intermediate. As  the builder in combination with jemalloc are very efficient in building up non-chunked memory, it would be nice to directly use them in certain cases.
> The most useful builders are the [StringBuilder|https://github.com/apache/arrow/blob/5030e235047bdffabf6a900dd39b64eeeb96bdc8/cpp/src/arrow/builder.h#L714] and [DictionaryBuilder|https://github.com/apache/arrow/blob/5030e235047bdffabf6a900dd39b64eeeb96bdc8/cpp/src/arrow/builder.h#L872] as they provide functionality to create columns that are not easily constructed using NumPy methods in Python.
> The basic approach would be to wrap the C++ classes in https://github.com/apache/arrow/blob/master/python/pyarrow/includes/libarrow.pxd so that they can be used from Cython. Afterwards, we should start a new file {{python/pyarrow/builder.pxi}} where we have classes take typical Python objects like {{str}} and pass them on to the C++ classes. At the end, these classes should also return (Python accessible) {{pyarrow.Array}} instances.



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