Compare two lists and modify element if different-CodePudding

I want to create a new list by comparing two equal sized lists and keeping the value if they match, and setting it to a fixed value if they don't. For example, if I compared the following two lists with a fixed value of -1:

fixed_value = -1
a = [1,2,3,4,5]
b = [1,3,3,2,5]

The output here should be [1, -1, 3, -1, 5].

Is there any neat way to do so, perhaps using a list comprehension?

CodePudding user response：

You can use zip() and a list comprehension.

fixed_value = -1
a = [1,2,3,4,5]
b = [1,3,3,2,5]

result = [item1 if item1 == item2 else fixed_value for item1, item2 in zip(a, b)]
print(result) # Prints [1, -1, 3, -1, 5]

zip() produces an iterable of tuples, where the first element is (a[0], b[0]), the second is (a[1], b[1]), etc. Then, we can check the elements in these tuples for equality; if they're equal, we add the first element in our tuple to the list, else we output -1.

CodePudding user response：

You could use list comprehension and include an if statement to check your condition. This solution uses zip() to iterate both lists at the same time. zip() is a Python built-in is able to "(i)terate over several iterables in parallel, producing tuples with an item from each one.":

result = [
    a_element if a_element == b_element else fixed_value
    for a_element, b_element in zip(a, b)
]

Iterating both a and b at the same time, you compare the elements. If they're the same, just use one of them (they're equal), but in other case use your fixed_value.