[jira] [Created] (ARROW-2800) [Python] Unavailable Parquet column statistics from Spark-generated file

["Wes McKinney (JIRA)" <ji...@apache.org>]

Wes McKinney created ARROW-2800:
-----------------------------------

             Summary: [Python] Unavailable Parquet column statistics from Spark-generated file
                 Key: ARROW-2800
                 URL: https://issues.apache.org/jira/browse/ARROW-2800
             Project: Apache Arrow
          Issue Type: Bug
          Components: Python
    Affects Versions: 0.9.0
            Reporter: Robert Gruener
             Fix For: 0.10.0


I have a dataset generated by spark which shows it has statistics for the string column when using the java parquet-mr code (shown by using `parquet-tools meta`) however reading from pyarrow shows that the statistics for that column are not set.  I should not the column only has a single value, though it still seems like a problem that pyarrow can't recognize it (it can recognize statistics set for the long and double types).

See https://github.com/apache/arrow/files/2161147/metadata.zip for file example.

Pyarrow Code To Check Statistics:

{code}
from pyarrow import parquet as pq

meta = pq.read_metadata('/tmp/metadata.parquet')
# No Statistics For String Column, prints false and statistics object is None
print(meta.row_group(0).column(1).is_stats_set)
{code}

Example parquet-meta output:

{code}
file schema: spark_schema 
--------------------------------------------------------------------------------
int:         REQUIRED INT64 R:0 D:0
string:      OPTIONAL BINARY O:UTF8 R:0 D:1
float:       REQUIRED DOUBLE R:0 D:0

row group 1: RC:8333 TS:76031 OFFSET:4 
--------------------------------------------------------------------------------
int:          INT64 SNAPPY DO:0 FPO:4 SZ:7793/8181/1.05 VC:8333 ENC:PLAIN_DICTIONARY,BIT_PACKED ST:[min: 0, max: 100, num_nulls: 0]
string:       BINARY SNAPPY DO:0 FPO:7797 SZ:1146/1139/0.99 VC:8333 ENC:PLAIN_DICTIONARY,BIT_PACKED,RLE ST:[min: hello, max: hello, num_nulls: 4192]
float:        DOUBLE SNAPPY DO:0 FPO:8943 SZ:66720/66711/1.00 VC:8333 ENC:PLAIN,BIT_PACKED ST:[min: 0.0057611096964338415, max: 99.99811053829232, num_nulls: 0]
{code}

I realize the column only has a single value though it still seems like pyarrow should be able to read the statistics set. I made this here and not a JIRA since I wanted to be sure this is actually an issue and there wasnt a ticket already made there (I couldnt find one but I wanted to be sure). Either way I would like to understand why this is



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