python - 带有字符数组的 Numpy ufunc.at

Question

有没有办法使用 numpy ufunc.at(特别是 add.at)来连接字符串数组？ add.at 或 char.add.at 都不能用于字符串/字符数组。

该方法需要处理n维数组，所以先根据索引拆分再join不太理想

a = np.array(['a', 'b'])
ixs =  np.array([0, 1, 1])
vals = np.array(['e', 'f', 'g])

# Neither of these options work

np.add.at(a, ixs, vals)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-29-fb8e3bd48930> in <module>()
      2 ixs =  np.array([0, 1])
      3 vals = np.array(['e', 'e'])
----> 4 np.add.at(a, ixs, vals)

TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('<U1') dtype('<U1') dtype('<U1')



np.char.add.at(a, ixs, vals)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-30-e1bb1f7868dd> in <module>()
      2 ixs =  np.array([0, 1])
      3 vals = np.array(['e', 'e'])
----> 4 np.char.add.at(a, ixs, vals)

AttributeError: 'function' object has no attribute 'at'

期望的输出:['ae', 'bfg']

非常感谢!

Answer 1

In [279]: a = np.array(['a', 'b']) 
     ...: ixs =  np.array([0, 1, 1]) 
     ...: vals = np.array(['e', 'f', 'g']) 
     ...:                      

你的错误:

In [280]: np.char.add.at(a, ixs, vals)                                       
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-280-f06ad4d86cfb> in <module>
----> 1 np.char.add.at(a, ixs, vals)

AttributeError: 'function' object has no attribute 'at'

In [281]: np.add.at(a, ixs, vals)                                            
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-281-683423808141> in <module>
----> 1 np.add.at(a, ixs, vals)

TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('<U1') dtype('<U1') dtype('<U1')

但让我们尝试使用对象数据类型数组add.at。

In [282]: ao=a.astype(object)                                                
In [283]: ao                                                                 
Out[283]: array(['a', 'b'], dtype=object)
In [284]: vo=vals.astype(object)                                             
In [285]: vo                                                                 
Out[285]: array(['e', 'f', 'g'], dtype=object)
In [286]: np.add.at(ao, ixs, vo)                                                                                                                
In [287]: ao                                                                 
Out[287]: array(['ae', 'bfg'], dtype=object)

numpy ufuncs 倾向于(总是？)通过将操作委托(delegate)给对象的相应方法来操作对象 dtype 数组。 add 是为 Python 字符串定义的，因此 add.at 可以按需要工作。