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https://issues.apache.org/jira/browse/ARROW-17774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17624677#comment-17624677
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Weston Pace commented on ARROW-17774:
-------------------------------------
The underlying issues appears to have been solved. I just checked that this
indeed works with the CSV writer:
{noformat}
import decimal
import pyarrow as pa
import pyarrow.compute as pc
import pyarrow.csv as csv
decimals = pa.array([decimal.Decimal(1), decimal.Decimal(0.3)])
small_decimals = pc.cast(decimals, pa.decimal256(12, 6), safe=False)
table = pa.Table.from_pydict({"rownum": [1, 2], "decimal": small_decimals})
csv.write_csv(table, '/tmp/foo.csv')
with open('/tmp/foo.csv') as f:
print(f.read())
# "rownum","decimal"
# 1,1.000000
# 2,0.299999
{noformat}
Do we want to add any pyarrow tests? Or just close this.
> [Python] write csv decimal cast error
> -------------------------------------
>
> Key: ARROW-17774
> URL: https://issues.apache.org/jira/browse/ARROW-17774
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Affects Versions: 8.0.0
> Reporter: Alejandro Marco Ramos
> Priority: Major
>
> Hi, when try to write table with any field in `Decimal128` type, arrow raises
> with this message:
> {code:java}
> In [136]: ds.write_dataset(table, "data", format="csv")
> ---------------------------------------------------------------------------
> ArrowNotImplementedError Traceback (most recent call last)
> Cell In [136], line 1
> ----> 1 ds.write_dataset(table, "data", format="csv")
> File
> c:\users\documents\projects\.venv\lib\site-packages\pyarrow\dataset.py:930,
> in write_dataset(data, base_dir, basename_template, format, partitioning,
> partitioning_flavor, schema, filesystem, file_options, use_threads,
> max_partitions, max_open_files, max_rows_per_file, min_rows_per_group,
> max_rows_per_group, file_visitor, existing_data_behavior, create_dir)
> 927 raise ValueError("Cannot specify a schema when writing a
> Scanner")
> 928 scanner = data
> --> 930 _filesystemdataset_write(
> 931 scanner, base_dir, basename_template, filesystem, partitioning,
> 932 file_options, max_partitions, file_visitor,
> existing_data_behavior,
> 933 max_open_files, max_rows_per_file,
> 934 min_rows_per_group, max_rows_per_group, create_dir
> 935 )
> File
> c:\users\documents\projects\.venv\lib\site-packages\pyarrow\_dataset.pyx:2737,
> in pyarrow._dataset._filesystemdataset_write()
> File
> c:\users\documents\projects\.venv\lib\site-packages\pyarrow\error.pxi:121, in
> pyarrow.lib.check_status()
> ArrowNotImplementedError: Unsupported cast from decimal128(21, 15) to utf8
> using function cast_string{code}
> my data is:
> {noformat}
> In [137]: table
> Out[137]:
> pyarrow.Table
> col1: int64
> col2: double
> col3: decimal128(21, 15)
> col4: string
> ----
> col1: [[1,2,3,0]]
> col2: [[2.7,0,3.24,3]]
> col3: [[-304236.460000000000000,0.E-15,0.E-15,0.E-15]]
> col4: [["primera","segunda","tercera","cuarta"]]{noformat}
>
> Thanks in advance.
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