np.array中的广播函数调用 [英] Broadcasting function calls in np.array

问题描述

我正在尝试创建一个充满对象的NumPy数组，我想知道是否有一种方法可以将每个对象广播到整个数组以做某事.

I am trying creating an NumPy array filled with an object, and I was wondering if there was a way I could broadcast to the entire array for each object to do something.

代码:

class player:
    def __init__(self,num = 5):
        self.num = num

    def printnum():
        print(self.num)
...

objs = np.array([player(5),player(6)],dtype=Object)
objs.printnum()

按原样返回错误.我尝试按照手册将dtype更改为:_object，但似乎没有任何作用.

As it stands this returns an error. I have tried changing the dtype to: _object as per the manual, but nothing seems to work.

推荐答案

numpy对象数组不继承该对象的方法. ndarray 方法通常作用于整个数组

A numpy array of objects does not inherit the methods of that object. ndarray methods in general act on the entire array

这对于内置类型也不起作用，例如:

This does not work for built-in types either, e.g.:

In [122]: import numpy as np

In [123]: n = 4.0

In [124]: a = np.arange(n)

In [125]: n.is_integer()
Out[125]: True

In [126]: a.is_integer()
---------------------------------------------------------------------------
AttributeError: 'numpy.ndarray' object has no attribute 'is_integer'

用元素运算符进行数字广播，例如加法运算:

Numpy broadcasting is done with element-wise operators, for example addition:

In [127]: n
Out[127]: 4.0

In [128]: a
Out[128]: array([ 0.,  1.,  2.,  3.])

In [129]: n + a
Out[129]: array([ 4.,  5.,  6.,  7.])

如果要对数组中的所有元素基本调用 print ，则可以简单地重新定义 .__ repr __()方法，该方法由 print调用.我会警告您，您将通过覆盖该方法而丢失信息.

If you want to basically call print on all the elements in your array, you could simply redefine the .__repr__() method which is called by print. I would caution you that you will lose information by overriding the method.

In [148]: class player:
   .....:     def __init__(self, num=5):
   .....:         self.num = num
   .....:     def __repr__(self):
   .....:         return str(self.num)
   .....:     

In [149]: objs = np.array([player(5), player(6)])

In [150]: objs
Out[150]: array([5, 6], dtype=object)

In [151]: print objs
[5 6]

尽管看起来像，但它与 np.array([5,6])不同:

Even though it looks like it, this is not the same as np.array([5,6]) though:

In [152]: objs * 3
----------------------
TypeError: unsupported operand type(s) for *: 'instance' and 'int'

在那里，您会看到覆盖 __ repr __ 的缺点.

And there you can see the disadvantage of overriding __repr__.

更简单的方法是使用当前的 printnum()方法，但要在循环中调用它:

The simpler way to do this is to use your current printnum() method, but call it in a loop:

In [164]: class player:
   .....:     def __init__(self, num=5):
   .....:         self.num = num
   .....:     def printnum(self):
   .....:         print(self.num)
   .....:         

In [165]: for p in objs:
   .....:     p.printnum()
   .....:
5
6

或者，也许定义您的方法以返回一个字符串而不是打印一个字符串，然后进行列表理解:

Or, perhaps define your method to return a string rather than print one, then make a list comprehension:

In [169]: class player:
   .....:     def __init__(self, num=5):
   .....:         self.num = num
   .....:     def printnum(self):
   .....:         return str(self.num)
   .....: 

In [170]: objs = np.array([player(5), player(6)])

In [171]: [p.printnum() for p in objs]
Out[171]: ['5', '6']

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