将Numpy结构数组保存到* .mat文件 [英] Saving Numpy Structure Array to *.mat file

问题描述

我正在使用numpy.loadtext从CSV数据文件生成结构化的Numpy数组，我想将其保存到MAT文件中，以供比Python更熟悉MATLAB的同事使用.

I am using numpy.loadtext to generate a structured Numpy array from a CSV data file that I would like to save to a MAT file for colleagues who are more familiar with MATLAB than Python.

示例案例:

import numpy as np
import scipy.io

mydata = np.array([(1, 1.0), (2, 2.0)], dtype=[('foo', 'i'), ('bar', 'f')])
scipy.io.savemat('test.mat', mydata)

当我尝试在此数组上使用scipy.io.savemat时，将引发以下错误:

When I attempt to use scipy.io.savemat on this array, the following error is thrown:

Traceback (most recent call last):
  File "C:/Project Data/General Python/test.py", line 6, in <module>
    scipy.io.savemat('test.mat', mydata)
  File "C:\python35\lib\site-packages\scipy\io\matlab\mio.py", line 210, in savemat
    MW.put_variables(mdict)
  File "C:\python35\lib\site-packages\scipy\io\matlab\mio5.py", line 831, in put_variables
    for name, var in mdict.items():
AttributeError: 'numpy.ndarray' object has no attribute 'items'

我是一名Python新手(充其量)，但是我认为这是因为savemat已设置为处理字典，并且Numpy的结构化数组的结构不兼容.

I'm a Python novice (at best), but I'm assuming this is because savemat is set up to handle dicts and the structure of Numpy's structured arrays is not compatible.

我可以通过将数据提取到字典中来解决此错误:

I can get around this error by pulling my data into a dict:

tmp = {}
for varname in mydata.dtype.names:
    tmp[varname] = mydata[varname]

scipy.io.savemat('test.mat', tmp)

哪些可以很好地加载到MATLAB中?

Which loads into MATLAB fine:

>> mydata = load('test.mat')

mydata = 

    foo: [1 2]
    bar: [1 2]

但是，这似乎是一种效率很低的方法，因为我正在复制内存中的数据.有没有更聪明的方法可以做到这一点?

But this seems like a very inefficient method since I'm duplicating the data in memory. Is there a smarter way to accomplish this?

推荐答案

您可以执行scipy.io.savemat('test.mat', {'mydata': mydata}).

这将在文件中创建具有字段foo和bar的结构mydata.

This creates a struct mydata with fields foo and bar in the file.

或者，您可以将循环打包到dict理解中:

Alternatively, you can pack your loop in a dict comprehension:

tmp = {varname: mydata[varname] for varname in mydata.dtype.names}

我不认为创建临时字典会在内存中复制数据，因为Python通常只存储引用，尤其是numpy会尝试尽可能地在原始数据中创建视图.

I don't think creating a temprorary dictionary duplicates data in memory, because Python generally only stores references, and numpy in particular tries to create views into the original data whenever possible.

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