在python 3中将地图对象转换为numpy数组 [英] Convert map object to numpy array in python 3

问题描述

在Python 2中，我可以执行以下操作:

In Python 2 I could do the following:

import numpy as np    
f = lambda x: x**2
seq = map(f, xrange(5))
seq = np.array(seq)
print seq
# prints: [ 0  1  4  9 16]

在Python 3中，它不再起作用:

In Python 3 it does not work anymore:

import numpy as np    
f = lambda x: x**2
seq = map(f, range(5))
seq = np.array(seq)
print(seq)
# prints: <map object at 0x10341e310>

如何获得旧的行为(将map结果转换为numpy数组)?

How do I get the old behaviour (converting the map results to numpy array)?

编辑:正如@jonrsharpe在他的回答中指出的，如果我先将seq转换为列表，则可以解决此问题:

Edit: As @jonrsharpe pointed out in his answer this could be fixed if I converted seq to a list first:

seq = np.array(list(seq))

但是我希望避免额外调用list.

but I would prefer to avoid the extra call to list.

推荐答案

除了@jonrsharpe已经指出的有效解决方案之外，还有另一种选择是使用

One more alternative, other than the valid solutions @jonrsharpe already pointed out is to use np.fromiter:

>>> import numpy as np    
>>> f = lambda x: x**2
>>> seq = map(f, range(5))
>>> np.fromiter(seq, dtype=np.int)
array([ 0,  1,  4,  9, 16])

这篇关于在python 3中将地图对象转换为numpy数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！