> from numpy import *
> a=array([[1,2],[3,4],[5,6]])
> a
array([[1, 2],
    [3, 4],
    [5, 6]])
> a.flatten() #默认按行的方向降维
array([1, 2, 3, 4, 5, 6])
> a.flatten('F') #按列降维
array([1, 3, 5, 2, 4, 6]) 
> a.flatten('A') #按行降维
array([1, 2, 3, 4, 5, 6])
>

> a=mat([[1,2,3],[4,5,6]])
> a
matrix([[1, 2, 3],
    [4, 5, 6]])
> a.flatten()
matrix([[1, 2, 3, 4, 5, 6]])
> a=mat([[1,2,3],[4,5,6]])
> a
matrix([[1, 2, 3],
    [4, 5, 6]])
> a.flatten()
matrix([[1, 2, 3, 4, 5, 6]])
> y=a.flatten().A 
> shape(y)
(1L, 6L)
> shape(y[0]) 
(6L,)
> a.flatten().A[0] 
array([1, 2, 3, 4, 5, 6])
> 

> a=array([[1,2],[3,4],[5,6]])
> [y for x in a for y in x]
[1, 2, 3, 4, 5, 6]
> 
！

> a = [[1,3],[2,4],[3,5]]
> a = array(a)
> a.flatten()
array([1, 3, 2, 4, 3, 5])

> a = [[1,3],[2,4],[3,5]]
> a.flatten()

Traceback (most recent call last):
 File "<pyshell#10>", line 1, in <module>
  a.flatten()
AttributeError: 'list' object has no attribute 'flatten'

> a = [[1,3],[2,4],[3,5],["abc","def"]]
> a1 = [y for x in a for y in x]
> a1
[1, 3, 2, 4, 3, 5, 'abc', 'def']

> a = [[1,3],[2,4],[3,5],["abc","def"]]
> flatten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else [x]
> flatten(a)
[1, 3, 2, 4, 3, 5, 'abc', 'def']

> a = [[1,3],[2,4],[3,5]]
> a = mat(a)
> y = a.flatten()
> y
matrix([[1, 3, 2, 4, 3, 5]])
> y = a.flatten().A
> y
array([[1, 3, 2, 4, 3, 5]])
> shape(y)
(1, 6)
> shape(y[0])
(6,)
> y = a.flatten().A[0]
> y
array([1, 3, 2, 4, 3, 5])