How to read parquet file with a condition using pyarrow in Python

问题

I have created a parquet file with three columns (id, author, title) from database and want to read the parquet file with a condition (title='Learn Python'). Below mentioned is the python code which I am using for this POC.

import pyarrow as pa
import pyarrow.parquet as pq
import pandas as pd
import pyodbc

def write_to_parquet(df, out_path, compression='SNAPPY'):
arrow_table = pa.Table.from_pandas(df)
if compression == 'UNCOMPRESSED':
    compression = None
pq.write_table(arrow_table, out_path, use_dictionary=False,
               compression=compression)

def read_pyarrow(path, nthreads=1):
return pq.read_table(path, nthreads=nthreads).to_pandas()


path = './test.parquet'
sql = "SELECT * FROM [dbo].[Book] (NOLOCK)"

conn = pyodbc.connect(r'Driver={SQL 
Server};Server=.;Database=APP_BBG_RECN;Trusted_Connection=yes;')
df = pd.io.sql.read_sql(sql, conn)

write_to_parquet(df, path)

df1 = read_pyarrow(path)

How can I put a condition (title='Learn Python') in read_pyarrow method?

回答1:

This is not yet supported. We intend to develop this functionality in the future. I recommend doing the filtering with pandas after the conversion from Arrow table.

来源：https://stackoverflow.com/questions/48714803/how-to-read-parquet-file-with-a-condition-using-pyarrow-in-python