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https://issues.apache.org/jira/browse/NIFI-1280?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15325013#comment-15325013
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Mark Payne commented on NIFI-1280:
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[~Toivo Adams] correct - the data would only be read multiple times if 
necessary but this won't normally happen. I spent some time looking at this a 
few days ago, actually, looking for a way to refactor it so that we can easily 
enable multi-pass reading. Unfortunately, though, the only solutions that I 
came up with are either very hack-y or would require some changes to the NiFi 
API in order to allow us to obtain an InputStream and return it outside of a 
ProcessSession callback, which I'm not wild about. Planned to revisit again 
next week, but just trying to figure out a good way to make this feasible.

> Create FilterCSVColumns Processor
> ---------------------------------
>
>                 Key: NIFI-1280
>                 URL: https://issues.apache.org/jira/browse/NIFI-1280
>             Project: Apache NiFi
>          Issue Type: Task
>          Components: Extensions
>            Reporter: Mark Payne
>            Assignee: Toivo Adams
>
> We should have a Processor that allows users to easily filter out specific 
> columns from CSV data. For instance, a user would configure two different 
> properties: "Columns of Interest" (a comma-separated list of column indexes) 
> and "Filtering Strategy" (Keep Only These Columns, Remove Only These Columns).
> We can do this today with ReplaceText, but it is far more difficult than it 
> would be with this Processor, as the user has to use Regular Expressions, 
> etc. with ReplaceText.
> Eventually a Custom UI could even be built that allows a user to upload a 
> Sample CSV and choose which columns from there, similar to the way that Excel 
> works when importing CSV by dragging and selecting the desired columns? That 
> would certainly be a larger undertaking and would not need to be done for an 
> initial implementation.



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