[jira] [Commented] (ARROW-17828) Large strings cause ArrowInvalid: offset overflow while concatenating arrays

["David Li (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-17828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17608754#comment-17608754 ] 

David Li commented on ARROW-17828:
----------------------------------

It's because Arrow string arrays have a 2 GiB limit due to the representation (each element is represented by 32-bit signed offsets into a backing buffer); you can cast to large_string first to avoid this (this uses 64-bit offsets) but I think the error here could be much improved (it should at least tell you what to do)

> Large strings cause ArrowInvalid: offset overflow while concatenating arrays
> ----------------------------------------------------------------------------
>
>                 Key: ARROW-17828
>                 URL: https://issues.apache.org/jira/browse/ARROW-17828
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>    Affects Versions: 9.0.0
>            Reporter: Ben Epstein
>            Priority: Major
>
> When working with medium-sized datasets that have very long strings, arrow fails when trying to operate on the strings. The root is the `combine_chunks` function.
> Here is a minimally reproducible example
> {code:java}
> import numpy as np
> import pyarrow as pa
> # Create a large string
> x = str(np.random.randint(low=0,high=1000, size=(30000,)).tolist())
> t = pa.chunked_array([x]*20_000)
> # Combine the chunks into large string array - fails
> combined = t.combine_chunks(){code}
> I get the following error
> {code:java}
> --------------------------------------------------------------------------- ArrowInvalid Traceback (most recent call last) /var/folders/x6/00594j4s2yv3swcn98bn8gxr0000gn/T/ipykernel_95780/4128956270.py in <module> ----> 1 z=t.combine_chunks()
> ~/.venv/lib/python3.7/site-packages/pyarrow/table.pxi in pyarrow.lib.ChunkedArray.combine_chunks() 
> ~/.venv/lib/python3.7/site-packages/pyarrow/array.pxi in pyarrow.lib.concat_arrays() ~/Documents/Github/dataquality/.venv/lib/python3.7/site-packages/pyarrow/error.pxi in pyarrow.lib.pyarrow_internal_check_status() ~.venv/lib/python3.7/site-packages/pyarrow/error.pxi in pyarrow.lib.check_status() 
> ArrowInvalid: offset overflow while concatenating arrays {code}
> With smaller strings or smaller arrays this works fine.
> {code:java}
> x = str(np.random.randint(low=0,high=1000, size=(10,)).tolist())
> t = pa.chunked_array([x]*1000)
> combined = t.combine_chunks(){code}
> The first example that fails takes a few minutes to run. If you'd like a faster example for experimentation, you can use `vaex` to generate the chunked array much faster. This will throw the identical error and will run about 1 second.
> {code:java}
> import vaex
> import numpy as np
> n = 50_000
> x = str(np.random.randint(low=0,high=1000, size=(30_000,)).tolist())
> df = vaex.from_arrays(
>     id=list(range(n)),
>     y=np.random.randint(low=0,high=1000,size=n)
> )
> df["text"] = vaex.vconstant(x, len(df))
> # text_chunk_array is now a pyarrow.lib.ChunkedArray
> text_chunk_array = df.text.values
> x = text_chunk_array.combine_chunks() {code}
>  
>  
>  



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