Python numpy 等价于 list.pop？
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numpy-equivalent of list.pop?
提问by Anton Alice
Is there a numpy method which is equivalent to the builtin popfor python lists?
是否有一个 numpy 方法相当于poppython 列表的内置方法？
Popping obviously doesn't work on numpy arrays, and I want to avoid a list conversion.
弹出显然不适用于 numpy 数组，我想避免列表转换。
回答by unutbu
There is no popmethod for NumPy arrays, but you could just use basic slicing (which would be efficient since it returns a view, not a copy):
popNumPy 数组没有方法，但您可以只使用基本切片（这将是有效的，因为它返回一个视图，而不是一个副本）：
In [104]: y = np.arange(5); y
Out[105]: array([0, 1, 2, 3, 4])
In [106]: last, y = y[-1], y[:-1]
In [107]: last, y
Out[107]: (4, array([0, 1, 2, 3]))
If there were a popmethod it would return the lastvalue in yand modify y.
如果有一个pop方法，它会返回last值y并修改y。
Above,
以上，
last, y = y[-1], y[:-1]
assigns the last value to the variable lastand modifies y.
将最后一个值赋给变量last并修改y.
回答by mozlingyu
Here is one example using numpy.delete():
这是一个使用示例numpy.delete()：
import numpy as np
arr = np.array([[1,2,3,4], [5,6,7,8], [9,10,11,12]])
print(arr)
# array([[ 1, 2, 3, 4],
# [ 5, 6, 7, 8],
# [ 9, 10, 11, 12]])
arr = np.delete(arr, 1, 0)
print(arr)
# array([[ 1, 2, 3, 4],
# [ 9, 10, 11, 12]])
回答by dbouz
Pop doesn't exist for NumPy arrays, but you can use NumPy indexing in combination with array restructuring, for example hstack/vstack or numpy.delete(), to emulate popping.
NumPy 数组不存在 Pop，但您可以将 NumPy 索引与数组重组（例如 hstack/vstack 或 numpy.delete()）结合使用来模拟弹出。
Here are some example functions I can think of (which apparently don't work when the index is -1, but you can fix this with a simple conditional):
以下是我能想到的一些示例函数（当索引为 -1 时显然不起作用，但您可以使用简单的条件来解决此问题）：
def poprow(my_array,pr):
""" row popping in numpy arrays
Input: my_array - NumPy array, pr: row index to pop out
Output: [new_array,popped_row] """
i = pr
pop = my_array[i]
new_array = np.vstack((my_array[:i],my_array[i+1:]))
return [new_array,pop]
def popcol(my_array,pc):
""" column popping in numpy arrays
Input: my_array: NumPy array, pc: column index to pop out
Output: [new_array,popped_col] """
i = pc
pop = my_array[:,i]
new_array = np.hstack((my_array[:,:i],my_array[:,i+1:]))
return [new_array,pop]
This returns the array without the popped row/column, as well as the popped row/column separately:
这将返回没有弹出行/列的数组，以及分别弹出的行/列：
>>> A = np.array([[1,2,3],[4,5,6]])
>>> [A,poparow] = poprow(A,0)
>>> poparow
array([1, 2, 3])
>>> A = np.array([[1,2,3],[4,5,6]])
>>> [A,popacol] = popcol(A,2)
>>> popacol
array([3, 6])
