有没有一种方法可以将一个巨大的parquet文件分成较小的文件(使用Python)?保留所有列并划分行?
谢谢import dask.dataframe as dd
ddf = dd.read_parquet('my_file.parquet')
ddf.repartition(3).to_parquet('my_files/')
编辑:您需要安装fastparquet
或pyarrow
之一。
由于使用Dask的答案仅适用于文件大小适合计算机RAM的情况,因此我将分享使用Pyarrow的脚本,并逐页读取文件:
import os
import pyarrow as pa
import pyarrow.parquet as pq
from pyarrow import Schema
class ParquetSplitter:
def __init__(self,
src_parquet_path: str,
target_dir: str,
num_chunks: int = 25
):
self._src_parquet_path = src_parquet_path
self._target_dir = target_dir
self._num_chunks = num_chunks
self._src_parquet = pq.ParquetFile(
self._src_parquet_path,
memory_map=True,
)
self._total_group_num = self._src_parquet.num_row_groups
self._schema = self._src_parquet.schema
@property
def num_row_groups(self):
print(f'Total num of groups found: {self._total_group_num}')
return self._src_parquet.num_row_groups
@property
def schema(self):
return self._schema
def read_rows(self):
for elem in self._src_parquet.iter_batches(
columns=['player_id', 'played_at']):
elem: pa.RecordBatch
print(elem.to_pydict())
def split(self):
for chunk_num, chunk_range in self._next_chunk_range():
table = self._src_parquet.read_row_groups(row_groups=chunk_range)
file_name = f'chunk_{chunk_num}.parquet'
path = os.path.join(self._target_dir, file_name)
print(f'Writing chunk #{chunk_num}...')
pq.write_table(
table=table,
where=path,
)
def _next_chunk_range(self):
upper_bound = self.num_row_groups
chunk_size = upper_bound // self._num_chunks
chunk_num = 0
low, high = 0, chunk_size
while low < upper_bound:
group_range = list(range(low, high))
yield chunk_num, group_range
chunk_num += 1
low, high = low + chunk_size, high + chunk_size
if high > upper_bound:
high = upper_bound
@staticmethod
def _get_row_hour(row: pa.RecordBatch):
return row.to_pydict()['played_at'][0].hour
if __name__ == '__main__':
splitter = BngParquetSplitter(
src_parquet_path="path/to/Parquet",
target_dir="path/to/result/dir",
num_chunks=100,
)
splitter.split()
此外,您可以使用Pyspark或Apache Beam Python SDK来实现此目的。它们允许您以更高效的方式拆分文件,因为它们可以在多节点群集上运行。上述示例使用低级别的Pyarrow库,并利用一台机器上的一个进程,因此执行时间可能很长。
npartitions
不是一个有效的参数,你只需要输入3
。 - rjurney