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读书笔记 numpy入门第2章数组分裂

admin 11月 14, 2020 0

np.split

Split an array into multiple sub-arrays

向以上函数传递一个索引列表作为参数，索引列表记录的是分裂点位置：

x = [1, 2, 3, 99, 99, 3, 2, 1]
x1, x2, x3 = np.split(x, [3, 5])
print(x1, x2, x3)

[1 2 3] [99 99] [3 2 1]

https://docs.scipy.org/doc/numpy/reference/generated/numpy.split.html

参数：

ary
indices or sections
axis

1
2
3

x = np.arange(9.0)
np.split(x, 3)
array([ 0.,  1.,  2.]), array([ 3.,  4.,  5.]), array([ 6.,  7.,  8.])]

x = np.arange(8.0)
>>> np.split(x, [3, 5, 6, 10])
>>>[array([ 0.,  1.,  2.]),
    array([ 3.,  4.]),
    array([ 5.]),
    array([ 6.,  7.]),
    array([], dtype=float64)]

np.vsplit和np.hsplit

N 分裂点会得到 N + 1 个子数组。

grid = np.arange(16).reshape((4, 4))
grid

>>> array([[ 0,  1,  2,  3],
           [ 4,  5,  6,  7],
           [ 8,  9, 10, 11],
           [12, 13, 14, 15]])

upper, lower = np.vsplit(grid, [2])
print(upper)
print(lower)

>>>[[0 1 2 3]
   [4 5 6 7]]
  [[ 8 9 10 11]
  [12 13 14 15]]

left, right = np.hsplit(grid, [2])
print(left)
print(right)

>>>[[ 0  1]
    [ 4  5]
    [ 8  9]
    [12 13]]
   [[ 2  3]
    [ 6  7]
    [10 11]
    [14 15]]

https://docs.scipy.org/doc/numpy/reference/generated/numpy.vsplit.html

https://docs.scipy.org/doc/numpy/reference/generated/numpy.hsplit.html

np.dsplit

https://docs.scipy.org/doc/numpy/reference/generated/numpy.split.html

>>> x = np.arange(9.0)
>>> np.split(x, 3)

>>> [array([ 0.,  1.,  2.]), array([ 3.,  4.,  5.]), array([ 6.,  7.,  8.])]

>>> x = np.arange(8.0)
>>> np.split(x, [3, 5, 6, 10])


>>>[array([ 0.,  1.,  2.]),
    array([ 3.,  4.]),
    array([ 5.]),
    array([ 6.,  7.]),
    array([], dtype=float64)]