How do I compare two arrays in python?

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?

Amadan · Accepted Answer · 2021-05-27 01:19:44Z

2

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.

answered May 27, 2021 at 1:19

Amadan

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Comments

Pi Marillion · Accepted Answer · 2021-05-27 01:20:17Z

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])

answered May 27, 2021 at 1:20

Pi Marillion

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1 Comment

Amadan Over a year ago

Huh, np.maximum. Learn something new every day.

xexogil990 · Accepted Answer · 2021-05-27 01:24:18Z

1

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

answered May 27, 2021 at 1:24

xexogil990

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Comments

readtheforums · Accepted Answer · 2021-05-27 01:46:13Z

0

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)

edited May 27, 2021 at 1:46

answered May 27, 2021 at 1:31

readtheforums

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Comments

Jeremy · Accepted Answer · 2021-05-27 01:48:42Z

0

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))]

answered May 27, 2021 at 1:48

Jeremy

1

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