Implement RecordBatch::concat

[silathdiir]

Which issue does this PR close?

Closes #461 .

Rationale for this change

As described in the issue, tries to implement RecordBatch::concat according to https://github.com/apache/arrow-datafusion/blob/master/datafusion/src/physical_plan/coalesce_batches.rs#L232 .

What changes are included in this PR?

Adds a new function concat to struct RecordBatch, and test cases.

Are there any user-facing changes?

With this fix, a new RecordBatch could be created by concatenating multiple RecordBatches.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.10345% with 4 lines in your changes missing coverage. Please review.

Project coverage is 82.62%. Comparing base (f1fb2b1) to head (3a14809).
Report is 2894 commits behind head on master.

Files with missing lines	Patch %	Lines
arrow/src/record_batch.rs	93.10%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #537      +/-   ##
==========================================
+ Coverage   82.60%   82.62%   +0.01%     
==========================================
  Files         167      167              
  Lines       45984    46042      +58     
==========================================
+ Hits        37984    38041      +57     
- Misses       8000     8001       +1     

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[alamb]

Thank you @silathdiir !

I think the error handling should be more strict when the schemas don't match, but otherwise this looks great

It looks like @jorgecarleitao #461 (comment) has a suggestion to move this function to arrow::compute::concat::concat_batches rather than in record_batch.rs. What do you think?

[alamb]

Although @nevi-me seems to like RecordBatch::concat -- #461 (comment)

[silathdiir]

Hi @alamb, refer to @jorgecarleitao latest comment #461 (comment), it seems that arrow::compute::concat::concat_batches may be better (even seems not good enough for thread model).
I will follow the discussion and try to update this PR.

[alamb]

I think this PR looks good to merge from my perspective, but I am not sure if we should move the concat function to arrow::compute . @jorgecarleitao nd @nevi-me what do you think we should do here?

[alamb]

thanks @silathdiir !

[alamb]

Unless I hear different, I plan to merge this PR tomorrow (and include it in 5.0.0)

[alamb]

Thanks again @silathdiir !