如何比较 python 中的两个 arrays？

Question

Suppose I have two arrays

array1=np.array([1,2,3,4,5,6,7,8,9,10])
array2=np.array([11,1,2,4,10,60,0,3,20,33])

I want to compare the two arrays and store the values that are bigger. I want to write a code that will check the first element of array1 with the first element of array2 and store the greatest value between them in a new array and so on.

I tried it with this code

array3=[]
i=0
while i<=len(array1):
    if array1[i]>array2[i]:
        array3.append(i)

However, the code doesn't give any output and keeps on running. The two array in question that i want to work with are very big so will a normal loop method work for big arrays as well?

Answer 1

If you're using numpy, using numpy all the way is preferable. It will be faster, and use less memory, than the iterative approach (and is more readable, too).

np.max([array1, array2], axis=0)

Your loop is infinite because your i never changes. If you fix that (either by adding i += 1 or by using for i in range(0, len(array1)): ), you will only be appending elements where array1 one is larger, and leaving out any pairs where they are equal, or where the array2 one is larger: an else: would be needed.

Answer 2

You're probably looking for something like numpy.maximum :

import numpy as np

array1 = np.array([ 1, 2, 3, 4,  5,  6, 7, 8, 9,  10])
array2 = np.array([11, 1, 2, 4, 10, 60, 0, 3, 20, 33])

np.maximum(array1, array2)
# array([11,  2,  3,  4, 10, 60,  7,  8, 20, 33])

Answer 3

A couple of things:

First, the reason it keeps going is that you are not incrementing your iterator i .

Second, currently you are adding the index of the greater number, and not the greater number. Try the following code(pure python):

array3 = []
i = 0
while i < len(array1):
    if array1[i] > array2[i]:
        array3.append(array1[i])
    else:
        array3.append(array2[i])
    i += 1

Answer 4

This should work!

import numpy as np

array1=np.array([1,2,3,4,5,6,7,8,9,10])
array2=np.array([11,1,2,4,10,60,0,3,20,33])

array3=[]
i=0
while i<len(array1):
    if array1[i]>array2[i]:
        array3.append(array1[i])
    else:
        array3.append(array2[i])
    i += 1

print(array3)

Answer 5

Wanted to do this with a list comprehension. This would work assuming the arrays are always the same size.

[max([array1[i],array2[i]]) for i in range(len(array1))]