1 numpy.insert
numpy.insert可以有三个参数(arr,obj,values),也可以有4个参数(arr,obj,values,axis):
第一个参数arr是一个数组,可以是一维的也可以是多维的,在arr的基础上 插入元素
第二个参数obj是元素插入的位置
第三个参数values是需要插入的数值
第四个参数axis是指示在哪一个轴上对应的插入位置进行插入
以下几点说明:
1)axis=0:从行方向插入
axis=1:从列方向插入
2)如果是多维数据,假如a=[N,C,H,W],N为行方向,C为列方向,每次只能插入一列或者一行,无法插入多行或者多列的数组
3)obj是元素插入位置,可以是多个位置插入,待插入值和values中的值对应
官方相关example
Examples
--------
>>> a = np.array([[1, 1], [2, 2], [3, 3]])
>>> a
array([[1, 1],
[2, 2],
[3, 3]])
>>> np.insert(a, 1, 5)
array([1, 5, 1, 2, 2, 3, 3])
>>> np.insert(a, 1, 5, axis=1)
array([[1, 5, 1],
[2, 5, 2],
[3, 5, 3]])
Difference between sequence and scalars:
>>> np.insert(a, [1], [[1],[2],[3]], axis=1)
array([[1, 1, 1],
[2, 2, 2],
[3, 3, 3]])
>>> np.array_equal(np.insert(a, 1, [1, 2, 3], axis=1),
... np.insert(a, [1], [[1],[2],[3]], axis=1))
True
>>> b = a.flatten()
>>> b
array([1, 1, 2, 2, 3, 3])
>>> np.insert(b, [2, 2], [5, 6])
array([1, 1, 5, 6, 2, 2, 3, 3])
>>> np.insert(b, slice(2, 4), [5, 6])
array([1, 1, 5, 2, 6, 2, 3, 3])
>>> np.insert(b, [2, 2], [7.13, False]) # type casting
array([1, 1, 7, 0, 2, 2, 3, 3])
>>> x = np.arange(8).reshape(2, 4)
>>> idx = (1, 3)
>>> np.insert(x, idx, 999, axis=1)
array([[ 0, 999, 1, 2, 999, 3],
[ 4, 999, 5, 6, 999, 7]])
2 numpy.append
numpu.append(arr,values,axis=None)
功能:将values插入到目标arr的最后。
注意:When axis
is specified, values
must have the correct shape
Parameters
----------
arr : array_like
Values are appended to a copy of this array.
values : array_like
These values are appended to a copy of arr
. It must be of the
correct shape (the same shape as arr
, excluding axis
). If
axis
is not specified, values
can be any shape and will be
flattened before use.
axis : int, optional
The axis along which values
are appended. If axis
is not
given, both arr
and values
are flattened before use.
axis=0:从行方向插入
axis=1:从列方向插入
3 numpy.delete
delete(arr, obj, axis=None)
功能:返回一个删除指定轴后的新的数组
Parameters
----------
arr : array_like
Input array.
obj : slice, int or array of ints
Indicate which sub-arrays to remove.
axis : int, optional
The axis along which to delete the subarray defined by obj
.
If axis
is None, obj
is applied to the flattened array.
Examples
--------
>>> arr = np.array([[1,2,3,4], [5,6,7,8], [9,10,11,12]])
>>> arr
array([[ 1, 2, 3, 4],
[ 5, 6, 7, 8],
[ 9, 10, 11, 12]])
>>> np.delete(arr, 1, 0)
array([[ 1, 2, 3, 4],
[ 9, 10, 11, 12]])
>>> np.delete(arr, np.s_[::2], 1)
array([[ 2, 4],
[ 6, 8],
[10, 12]])
>>> np.delete(arr, [1,3,5], None)
array([ 1, 3, 5, 7, 8, 9, 10, 11, 12])