创建视图以重新排列子类

Question

我想子类numpy rearrays并能够从该类创建视图。例如:

_Theta = np.dtype([('v', '<f8'), ('a', '<f8'), ('w', '<f8')])
class Theta(np.recarray):
    ''' Defines a class for the parameters of a DDM model. '''
    def __new__(clc, shape=1):
        return np.recarray.__new__(clc, shape, _Theta)

如果我创建一个实例，它会产生我想要的结果。

In [12]: r = Theta()
In [13]: r
Out[13]: 
Theta([(6.91957786449907e-310, 2.9958354e-316, 2.0922526e-316)], 
      dtype=[('v', '<f8'), ('a', '<f8'), ('w', '<f8')])

但是，如果我尝试创建类的视图，我会得到以下内容:

In [11]: np.zeros(3).view(Theta).a
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-11-b9bdab6cd66c> in <module>()
----> 1 np.zeros(3).view(Theta).a
/usr/lib/python2.7/dist-packages/numpy/core/records.pyc in __getattribute__(self, attr)
    414             res = fielddict[attr][:2]
    415         except (TypeError, KeyError):
--> 416             raise AttributeError("record array has no attribute %s" % attr)
    417         obj = self.getfield(*res)
    418         # if it has fields return a recarray, otherwise return
AttributeError: record array has no attribute a

是否有可能创建一个数组的视图，这样我就可以用我为Theta定义的属性来处理它们?(我认为这应该通过array_finalize方法以某种方式完成，但我不知道如何)。

Answer 1

可以这样实现:

import numpy as np
class Theta(np.recarray):
    ''' Defines a class for the parameters of a DDM model.
    '''
    def __new__(clc, *args, **kwargs):
        a = np.atleast_2d(np.array(*args, **kwargs))
        dtype = np.dtype([('v', '<f8'), ('a', '<f8'), ('w', '<f8')])
        r = np.recarray(shape=a.shape[0], dtype=dtype)
        r.v = a[:,0]
        r.a = a[:,1]
        r.w = a[:,2]
        return r.view(Theta)
r = Theta([[1,2,3],[1,2,3]])

这样:

a = Theta(np.zeros(3))

会做你想做的事…这可能需要额外的检查，如:

assert a.shape[1] % 3 == 0