[jira] [Commented] (ARROW-16616) [Python] Allow lazy evaluation of filters in Dataset and add Datset.filter method

["Will Jones (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-16616?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17557141#comment-17557141 ] 

Will Jones commented on ARROW-16616:
------------------------------------

I'm a little cautious about the idea of {{Dataset.filter()}} returning a {{Dataset}}, since it mixes up the purpose of {{Dataset}} and {{Scanner}}. If it did, what would this return then?

{code:python}
ds.filter(ds.field("x") > 2).scan(filter=ds.field("y") < 3)
{code}

I think it might be better if {{Dataset.filter()}} returned a scanner with that filter. And then {{Scanner}} could also have {{filter()}} and {{project()}} methods to allow chaining. What do you think of that?

> [Python] Allow lazy evaluation of filters in Dataset and add Datset.filter method
> ---------------------------------------------------------------------------------
>
>                 Key: ARROW-16616
>                 URL: https://issues.apache.org/jira/browse/ARROW-16616
>             Project: Apache Arrow
>          Issue Type: Sub-task
>          Components: Python
>            Reporter: Alessandro Molina
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 9.0.0
>
>          Time Spent: 0.5h
>  Remaining Estimate: 0h
>
> To keep the {{Dataset}} api compatible with the {{Table}} one in terms of analytics capabilities, we should add a {{Dataset.filter}} method. The initial POC was based on {{_table_filter}} but that required materialising all the {{Dataset}} content after filtering as it returned an {{{}InMemoryDataset{}}}. 
> Given that {{Scanner}} can filter a dataset without actually materialising the data until a final step happens, it would be good to have {{Dataset.filter}} return some form of lazy dataset when the filter is only stored aside and the Scanner is created when data is actually retrieved.
> PS: Also update {{test_dataset_filter}} test to use the {{Dataset.filter}} method



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