scipy.io.loadmat 嵌套结构(即字典)
使用给定的例程(如何使用 scipy 加载 Matlab .mat 文件),我无法访问更深的嵌套结构以将它们恢复到字典中
为了更详细地介绍我遇到的问题,我给出了以下玩具示例:
load scipy.io as spio
a = {'b':{'c':{'d': 3}}}
# my dictionary: a['b']['c']['d'] = 3
spio.savemat('xy.mat',a)
现在我想将 mat 文件读回到 python 中。我尝试了以下操作:
vig=spio.loadmat('xy.mat',squeeze_me=True)
如果我现在想访问我得到的字段:
>> vig['b']
array(((array(3),),), dtype=[('c', '|O8')])
>> vig['b']['c']
array(array((3,), dtype=[('d', '|O8')]), dtype=object)
>> vig['b']['c']['d']
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/<ipython console> in <module>()
ValueError: field named d not found.
但是,通过使用选项 struct_as_record=False
可以访问该字段:
v=spio.loadmat('xy.mat',squeeze_me=True,struct_as_record=False)
现在可以通过以下方式访问它:
>> v['b'].c.d
array(3)
Using the given routines (how to load Matlab .mat files with scipy), I could not access deeper nested structures to recover them into dictionaries
To present the problem I run into in more detail, I give the following toy example:
load scipy.io as spio
a = {'b':{'c':{'d': 3}}}
# my dictionary: a['b']['c']['d'] = 3
spio.savemat('xy.mat',a)
Now I want to read the mat-File back into python. I tried the following:
vig=spio.loadmat('xy.mat',squeeze_me=True)
If I now want to access the fields I get:
>> vig['b']
array(((array(3),),), dtype=[('c', '|O8')])
>> vig['b']['c']
array(array((3,), dtype=[('d', '|O8')]), dtype=object)
>> vig['b']['c']['d']
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/<ipython console> in <module>()
ValueError: field named d not found.
However, by using the option struct_as_record=False
the field could be accessed:
v=spio.loadmat('xy.mat',squeeze_me=True,struct_as_record=False)
Now it was possible to access it by
>> v['b'].c.d
array(3)
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只是对合并答案的增强,不幸的是,如果它到达对象的元胞数组,它将停止递归。以下版本将改为创建它们的列表,并在可能的情况下继续递归到元胞数组元素中。
import scipy.io as spio
import numpy as np
def loadmat(filename):
'''
this function should be called instead of direct spio.loadmat
as it cures the problem of not properly recovering python dictionaries
from mat files. It calls the function check keys to cure all entries
which are still mat-objects
'''
def _check_keys(d):
'''
checks if entries in dictionary are mat-objects. If yes
todict is called to change them to nested dictionaries
'''
for key in d:
if isinstance(d[key], spio.matlab.mat_struct):
d[key] = _todict(d[key])
return d
def _todict(matobj):
'''
A recursive function which constructs from matobjects nested dictionaries
'''
d = {}
for strg in matobj._fieldnames:
elem = matobj.__dict__[strg]
if isinstance(elem, spio.matlab.mat_struct):
d[strg] = _todict(elem)
elif isinstance(elem, np.ndarray):
d[strg] = _tolist(elem)
else:
d[strg] = elem
return d
def _tolist(ndarray):
'''
A recursive function which constructs lists from cellarrays
(which are loaded as numpy ndarrays), recursing into the elements
if they contain matobjects.
'''
elem_list = []
for sub_elem in ndarray:
if isinstance(sub_elem, spio.matlab.mat_struct):
elem_list.append(_todict(sub_elem))
elif isinstance(sub_elem, np.ndarray):
elem_list.append(_tolist(sub_elem))
else:
elem_list.append(sub_elem)
return elem_list
data = spio.loadmat(filename, struct_as_record=False, squeeze_me=True)
return _check_keys(data)
自 scipy >= 1.5.0< /a> 此功能现在使用 simplify_cells
参数内置。
from scipy.io import loadmat
mat_dict = loadmat(file_name, simplify_cells=True)
我在 scipy 邮件列表上得到了建议 (https://mail.python.org/pipermail/ scipy-user/)表明还有两种方法可以访问此数据。
这有效:
import scipy.io as spio
vig=spio.loadmat('xy.mat')
print vig['b'][0, 0]['c'][0, 0]['d'][0, 0]
在我的机器上输出:
3
这种访问的原因:“由于历史原因,在Matlab中,一切都至少是一个二维数组,甚至是标量。”
因此 scipy.io.loadmat 默认情况下模仿 Matlab 行为。
另一种有效的方法:
import scipy.io as spio
vig=spio.loadmat('xy.mat',squeeze_me=True)
print vig['b']['c'].item()['d']
输出:
3
我也在 scipy 邮件列表上学到了这个方法。我当然不明白(还)为什么必须添加 '.item()' ,并且:
print vig['b']['c']['d']
会抛出错误:
IndexError: only integers, slices (:
), ellipsis (< code>...)、numpy.newaxis (None
) 和整数或布尔数组是有效索引,
但当我知道时我会回来补充解释。 numpy.ndarray.item 的解释(来自 thenumpy 参考):
将数组的元素复制到标准 Python 标量并返回它。
(请注意,这个答案与 hpaulj 对最初问题的评论基本相同,但我觉得该评论不够“可见”或不够理解。当我为第一个问题搜索解决方案时,我当然没有注意到它时间,几周前)。
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以下是重建字典的函数,只需使用此 loadmat 而不是 scipy.io 的 loadmat:
Here are the functions, which reconstructs the dictionaries just use this loadmat instead of scipy.io's loadmat: