Python 如何创建一个元素都等于指定值的数组？
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How do I create an array whose elements are all equal to a specified value?
提问by maxm
How do I create an array where every entry is the same value? I know numpy.ones()and numpy.zeros()do this for 1's and 0's, but what about -1?
如何创建一个数组，其中每个条目的值都相同？我知道numpy.ones()并numpy.zeros()为 1 和 0 执行此操作，但是呢-1？
For example:
例如：
>>import numpy as np
>>np.zeros((3,3))
array([[ 1., 1., 1.],
[ 1., 1., 1.],
[ 1., 1., 1.]])
>>np.ones((2,5))
array([[ 1., 1., 1., 1., 1.],
[ 1., 1., 1., 1., 1.]])
>>np.negative_ones((2,5))
???
采纳答案by DSM
I don't know if there's a nice one-liner without an arithmetic operation, but probably the fastest approach is to create an uninitialized array using emptyand then use .fill()to set the values. For comparison:
我不知道是否有没有算术运算的不错的单行，但最快的方法可能是创建一个未初始化的数组empty，然后使用它.fill()来设置值。比较：
>>> timeit m = np.zeros((3,3)); m += -1
100000 loops, best of 3: 6.9 us per loop
>>> timeit m = np.ones((3,3)); m *= -1
100000 loops, best of 3: 9.49 us per loop
>>> timeit m = np.zeros((3,3)); m.fill(-1)
100000 loops, best of 3: 2.31 us per loop
>>> timeit m = np.empty((3,3)); m[:] = -1
100000 loops, best of 3: 3.18 us per loop
>>> timeit m = np.empty((3,3)); m.fill(-1)
100000 loops, best of 3: 2.09 us per loop
but to be honest, I tend to either add to the zero matrix or multiply the ones matrix instead, as initialization is seldom a bottleneck.
但老实说，我倾向于添加到零矩阵或乘以一个矩阵，因为初始化很少是瓶颈。
回答by Manish Mulani
-1 * np.ones((2,5))
-1 * np.ones((2,5))
Multplying by the number you need in the matrix will do the trick.
乘以矩阵中所需的数字即可。
In [5]: -1 * np.ones((2,5))
Out[5]:
array([[-1., -1., -1., -1., -1.],
[-1., -1., -1., -1., -1.]])
In [6]: 5 * np.ones((2,5))
Out[6]:
array([[ 5., 5., 5., 5., 5.],
[ 5., 5., 5., 5., 5.]])
回答by asheeshr
For an array of -1s
对于 -1 的数组
-1 * np.ones((2,5))
Simply multiply with the constant.
简单地乘以常数。
回答by Ramón J Romero y Vigil
foo = np.repeat(10, 50).reshape((5,10))
Will create a 5x10 matrix of 10s.
将创建一个 5x10 的 10 矩阵。
回答by learning
How about:
怎么样：
[[-1]*n]*m
where n is the number of columns and m is the number of rows?
其中 n 是列数，m 是行数？
