找到Python中最大的元素并与第一个元素交换

Question

我想找到r2中最大的元素，并将其与r2[0,0]中的元素交换。我给出了预期的输出。

import numpy as np
r2 = np.array([[  1.00657843,  63.38075613, 312.87746691],
[375.25164461, 500.        , 125.75493382],
[437.6258223 , 250.50328922, 188.12911152]])
indices = np.where(r2 == r2.max())

期望输出为

array([[  500.,  63.38075613, 312.87746691],
[375.25164461,  1.00657843, 125.75493382],
[437.6258223 , 250.50328922, 188.12911152]]

Answer 1

可以直接返回最大值的索引然后与第一个索引交换

# get index of largest value. 
index = np.unravel_index(r2.argmax(), r2.shape)
# swap with item at index 0,0
r2[index], r2[0,0] = r2[0,0], r2[index]

Answer 2

您可以将最大值存储在一个变量中，然后将[0, 0]元素分配给您在where中找到的索引，然后将[0, 0]元素设置为存储的最大值:

maximum = r2.max()
indices = np.where(r2 == maximum)
r2[indices] = r2[0, 0]
r2[0, 0] = maximum
r2

输出:

array([[500.        ,  63.38075613, 312.87746691],
[375.25164461,   1.00657843, 125.75493382],
[437.6258223 , 250.50328922, 188.12911152]])

Answer 3

这样你就可以替换所有具有max值的元素

#get the max value of the array
max_value = np.max(r2)
#all the element with the max value will be replaced with the first value
r2[r2 == max_value] = r2[0][0]
#put the max value in the first position
r2[0][0] = max_value