在Python中将二维数组变为一维数组

Question

我在尝试把一个数组“扁平化”，也就是把它转换成只有一维的项目集合。我使用了append命令，结果是这样的：

[['X', 'X'],['ff','ff','ff','ff','ff']]

不过我更希望这些元素能按以下方式排序：

['X','X','ff','ff','ff','ff','ff']

我不能使用string.join()或string.split()这些操作。那么，有什么更合理的方法来实现这个呢？

Answer 1

为了完整起见，总是有

In [1]: x = [['X', 'X'], ['ff', 'ff', 'ff', 'ff', 'ff']]
In [2]: sum(x, [])
Out[2]: ['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']

但是

In [3]: [item for sublist in x for item in sublist]
Out[3]: ['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']

应该会更快，并且

In [4]: from itertools import chain
In [5]: list(chain.from_iterable(x))
Out[5]: ['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']

应该是最快的。

Answer 2

可以使用 itertools.chain 或者 extend() 方法。

>>> from itertools import chain
>>> oldList = [['X', 'X'],['ff','ff','ff','ff','ff']]
>>> list(chain.from_iterable(oldList))
['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']

>>> list1 = ['X', 'X']
>>> list1.extend(['ff','ff','ff','ff','ff'])
>>> list1
['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']

Answer 3

使用列表推导式：

alist = [['X', 'X'],['ff','ff','ff','ff','ff']]
print [j for i in alist for j in i ]

使用reduce函数：

reduce(lambda r,x:r+x, alist,[])

输出结果：

['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']

Answer 4

我觉得你想要的是extend()而不是append()

>>> oldList = [['X', 'X'],['ff','ff','ff','ff','ff']]
>>> print oldList
[['X', 'X'], ['ff', 'ff', 'ff', 'ff', 'ff']]
>>> newList = []
>>> for item in oldList:
...     newList.extend( item )
>>> print newList
>>> ['X', 'X', 'ff', 'ff', 'ff', 'ff', 'ff']