将大 pandas 数据帧分块写入CSV文件 [英] Writing large Pandas Dataframes to CSV file in chunks
问题描述
如何将大数据文件分块写入CSV文件?
How do I write out a large data file to a CSV file in chunks?
我有一组大型数据文件(1M行x 20列).但是,我只关注该数据的5列左右.
I have a set of large data files (1M rows x 20 cols). However, only 5 or so columns of that data is of interest to me.
我想通过只用感兴趣的列制作这些文件的副本来使事情变得更容易,所以我可以使用较小的文件进行后期处理.因此,我计划将文件读取到数据帧中,然后再写入csv文件.
I want to make things easier by making copies of these files with only the columns of interest so I have smaller files to work with for post-processing. So I plan to read the file into a dataframe, then write to csv file.
我一直在研究将大数据文件以块的形式读取到数据帧中.但是,关于如何将数据分块写入csv文件方面,我一无所获.
I've been looking into reading large data files in chunks into a dataframe. However, I haven't been able to find anything on how to write out the data to a csv file in chunks.
这是我现在正在尝试的操作,但这不会附加csv文件:
Here is what I'm trying now, but this doesn't append the csv file:
with open(os.path.join(folder, filename), 'r') as src:
df = pd.read_csv(src, sep='\t',skiprows=(0,1,2),header=(0), chunksize=1000)
for chunk in df:
chunk.to_csv(os.path.join(folder, new_folder,
"new_file_" + filename),
columns = [['TIME','STUFF']])
推荐答案
解决方案:
header = True
for chunk in chunks:
chunk.to_csv(os.path.join(folder, new_folder, "new_file_" + filename),
header=header, cols=[['TIME','STUFF']], mode='a')
header = False
注意:
-
mode='a'
告诉熊猫追加. - 我们只在第一个块上写一个列标题.
- The
mode='a'
tells pandas to append. - We only write a column header on the first chunk.
这篇关于将大 pandas 数据帧分块写入CSV文件的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!