用偶数和奇数格式化 Numpy 数组

Question

我正在尝试编写一个代码，将sequence_numbers 中的偶数替换为正的init_val 值，并将每个奇数和0 值的变量替换为负的init_val 值。我怎么能编写这样的代码？

代码：

import numpy as np 
import pandas as pd 

sequence_numbers= np.array([1,0,4,7,9,12,15,16,22,2,4,8,11,13,11,21,23,3])

#The choice could be 'even', 'odd' or '0'
choice = 'even'
init_val = 100 

预期输出：

[-100, -100, 100, -100, -100, 100, -100,100, 100,
 100, 100, 100, -100, -100, -100, -100,  -100, -100 ]   

Answer 1

使用numpy.where 和模运算符来确定奇/偶状态。

“偶数”示例：

out = np.where(sequence_numbers%2, -init_val, init_val)

输出：

array([-100,  100,  100, -100, -100,  100, -100,  100,  100,  100,  100,
        100, -100, -100, -100, -100, -100, -100])

对于“奇数”，只需反转真/假值：

out = np.where(sequence_numbers%2, init_val, -init_val)

或逆向init_val:

if choice == 'odd':
    init_val *= -1
out = np.where(sequence_numbers%2, -init_val, init_val)

Answer 2

你可以使用：

out = (sequence_numbers % 2 * -2 + 1) * init_val
print(out)

# Output
array([-100,  100,  100, -100, -100,  100, -100,  100,  100,  100,  100,
        100, -100, -100, -100, -100, -100, -100])