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https://issues.apache.org/jira/browse/ARROW-3329?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17035562#comment-17035562
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Jacek Pliszka commented on ARROW-3329:
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The key question is whether CastFunctor in cast.cc has access to scale
of the decimal? If yes how?
If not - these are the options I've came up with:
Let's assume Decimal128Type value is n
Then I expect that base call
.cast('int64') will return overflow for n beyond int64 values, value otherwise
Option 1:
.cast('int64', decimal_scale=s) would calculate n/10**s and return
overflow if it is beyond int64, value otherwise
Option 2:
.cast('int64', bytes_group=0) would return n & 0x00000000FFFFFFFF
.cast('int64', bytes_group=1) would return (n >> 64) & 0x00000000FFFFFFFF
.cast('int64') would have default value bytes_group=0
Option 3:
cast has no CastOptions but we add multiply compute kernel and have
something like this instead:
.compute('multiply', 10**-s).cast('int64')
> [Python] Error casting decimal(38, 4) to int64
> ----------------------------------------------
>
> Key: ARROW-3329
> URL: https://issues.apache.org/jira/browse/ARROW-3329
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Environment: Python version : 3.6.5
> Pyarrow version : 0.10.0
> Reporter: Kavita Sheth
> Priority: Major
>
> Git issue LInk : https://github.com/apache/arrow/issues/2627
> I want to cast pyarrow table column from decimal(38,4) to int64.
> col.cast(pa.int64())
> Error:
> File "pyarrow/table.pxi", line 443, in pyarrow.lib.Column.cast
> File "pyarrow/error.pxi", line 89, in pyarrow.lib.check_status
> pyarrow.lib.ArrowNotImplementedError: No cast implemented from decimal(38,
> 4) to int64
> Python version : 3.6.5
> Pyarrow version : 0.10.0
> is it not implemented yet or I am not using it correctly? If not implemented
> yet, then any work around to cast columns?
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