Compare Arrays in Python

General Discussions
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1

How can I compare arrays in Python?

I have two strings:

date = "Thu Sep 16 13:14:15 CDT 2010"
sdate = "Thu Sep 16 14:14:15 CDT 2010"

I split these strings into lists using:

dateArr = date.split()
sdateArr = sdate.split()

Now, I want to compare these two arrays. In Java, I can do a simple comparison like dateArr[i] == sdateArr[i], but how can I perform the same comparison in Python?

2

Comparing arrays in Python is quite straightforward with the equality operator (==). It works element by element, so two lists are considered equal if their elements and order match perfectly:

a = [1, 2, 3]
b = ['a', 'b']
c = [1, 2, 3, 4]
d = [1, 2, 3]

print(a == b)  # False, different content
print(a == c)  # False, different length
print(a == d)  # True, same elements and order

If your arrays are simple, this approach is reliable for python compare arrays.

3

Building on that, if you’re comparing arrays where order doesn’t matter, you can convert the arrays to sets and compare them. This works because sets in Python are unordered collections of unique elements. For example:

a = [1, 2, 3]
b = [3, 2, 1]
are_equal = set(a) == set(b)
print(are_equal)  # True

Just keep in mind, this method ignores duplicates. For example:

c = [1, 2, 2, 3]
d = [1, 2, 3]
print(set(c) == set(d))  # True, duplicates are ignored

If ignoring duplicates is acceptable for python compare arrays, this is a good choice.

4

Great points so far! But if you want to maintain the order and handle duplicates, yet still do advanced comparisons, you can use modules like collections.Counter or create your own comparison logic. For example:

from collections import Counter

a = [1, 2, 2, 3]
b = [3, 2, 2, 1]
print(Counter(a) == Counter(b))  # True, same elements and counts

Or, you can perform element-wise comparisons using loops or list comprehensions:

dateArr = ['Thu', 'Sep', '16', '13:14:15', 'CDT', '2010']
sdateArr = ['Thu', 'Sep', '16', '14:14:15', 'CDT', '2010']

matches = [dateArr[i] == sdateArr[i] for i in range(len(dateArr))]
print(matches)  # [True, True, True, False, True, True]

This approach helps identify which elements differ when doing python compare arrays.