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[英]Pyspark dataframe splitting and saving by column values by using Parallel Processing
[英]pandas data frame splitting by column values using Parallel Processing
我有一個非常大的 pandas dataframe,我正在嘗試按股票名稱將它分成多個,並將它們保存到 csv。
stock date time spread time_diff
VOD 01-01 9:05 0.01 0:07
VOD 01-01 9:12 0.03 0:52
VOD 01-01 10:04 0.02 0:11
VOD 01-01 10:15 0.01 0:10
BAT 01-01 10:25 0.03 0:39
BAT 01-01 11:04 0.02 22:00
BAT 01-02 9:04 0.02 0:05
BAT 01-01 10:15 0.01 0:10
BOA 01-01 10:25 0.03 0:39
BOA 01-01 11:04 0.02 22:00
BOA 01-02 9:04 0.02 0:05
我知道如何以傳統方式做到這一點
def split_save(df):
ids = df['stock'].unique()
for id in ids:
df = df[df['stock']==id]
df.to_csv(f'{my_path}/{id}.csv')
但是,由於我有一個非常大的 dataframe 和數千只股票,我想進行多處理以加速。
任何想法? (稍后我可能還會嘗試 pyspark。)
謝謝 !
由於涉及 I/O,我不希望選擇 dataframe 成為主要阻塞點。
到目前為止,我可以為您提供兩種加快速度的解決方案:
線程:只需在不同的線程或ThreadPoolExecutor中啟動每只股票
def dump_csv(df, ticker):
df.groupby(ticker).to_csv(f'{my_path}/{ticker}.csv')
# We can use a with statement to ensure threads are cleaned up promptly
with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:
futures = {executor.submit(df, ticker):ticker for ticker in df['stock'].unique()}
for future in concurrent.futures.as_completed(futures):
print(f"Dumped ticker {futures[future]}")
(代碼未經測試,改編自示例)
在 ZIP 文件中工作:對於存儲許多文件,zip 檔案是一個很好的選擇,但它應該得到“讀者”的支持。
為了完整起見:
with ZipFile('stocks.zip', 'w', compression=zipfile.ZIP_DEFLATED) as zf:
ids = df['stock'].unique()
for id in ids:
zf.writestr(f'{id}.csv', df.groupby(ticker).to_csv())
我懷疑groupby
是阻礙你前進的原因,但對於寫作,我們可以通過這樣的multithreading
來加快速度:
from concurrent.futures import ThreadPoolExecutor
# Number of cores/threads your CPU has/that you want to use.
workers = 4
def save_group(grouped):
name, group = grouped
group.to_csv(f'{name}.csv')
with ThreadPoolExecutor(workers) as pool:
processed = pool.map(save_group, df.groupby('stock'))
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