更新时间:2023-02-27 09:20:18
是的,将 csv
文件读入 numpy
非常慢.沿着代码路径有很多纯 Python.这些天,即使我使用纯 numpy
我仍然使用 pandas
进行 IO:
或者,在这样一个足够简单的情况下,您可以使用类似 Joe Kington 写的内容此处:
>>>%time data = iter_loadtxt("test.csv")CPU 时间:用户 2.84 秒,系统:24 毫秒,总计:2.86 秒挂壁时间:2.86 秒还有 Warren Weckesser 的 textreader 库,以防 pandas
太重一个依赖:
I posted this question because I was wondering whether I did something terribly wrong to get this result.
I have a medium-size csv file and I tried to use numpy to load it. For illustration, I made the file using python:
import timeit
import numpy as np
my_data = np.random.rand(1500000, 3)*10
np.savetxt('./test.csv', my_data, delimiter=',', fmt='%.2f')
And then, I tried two methods: numpy.genfromtxt, numpy.loadtxt
setup_stmt = 'import numpy as np'
stmt1 = """
my_data = np.genfromtxt('./test.csv', delimiter=',')
"""
stmt2 = """
my_data = np.loadtxt('./test.csv', delimiter=',')
"""
t1 = timeit.timeit(stmt=stmt1, setup=setup_stmt, number=3)
t2 = timeit.timeit(stmt=stmt2, setup=setup_stmt, number=3)
And the result shows that t1 = 32.159652940464184, t2 = 52.00093725634724.
However, When I tried using matlab:
tic
for i = 1:3
my_data = dlmread('./test.csv');
end
toc
The result shows: Elapsed time is 3.196465 seconds.
I understand that there may be some differences in the loading speed, but:
Any input would be appreciated. Thanks a lot in advance!
Yeah, reading csv
files into numpy
is pretty slow. There's a lot of pure Python along the code path. These days, even when I'm using pure numpy
I still use pandas
for IO:
>>> import numpy as np, pandas as pd
>>> %time d = np.genfromtxt("./test.csv", delimiter=",")
CPU times: user 14.5 s, sys: 396 ms, total: 14.9 s
Wall time: 14.9 s
>>> %time d = np.loadtxt("./test.csv", delimiter=",")
CPU times: user 25.7 s, sys: 28 ms, total: 25.8 s
Wall time: 25.8 s
>>> %time d = pd.read_csv("./test.csv", delimiter=",").values
CPU times: user 740 ms, sys: 36 ms, total: 776 ms
Wall time: 780 ms
Alternatively, in a simple enough case like this one, you could use something like what Joe Kington wrote here:
>>> %time data = iter_loadtxt("test.csv")
CPU times: user 2.84 s, sys: 24 ms, total: 2.86 s
Wall time: 2.86 s
There's also Warren Weckesser's textreader library, in case pandas
is too heavy a dependency:
>>> import textreader
>>> %time d = textreader.readrows("test.csv", float, ",")
readrows: numrows = 1500000
CPU times: user 1.3 s, sys: 40 ms, total: 1.34 s
Wall time: 1.34 s