I am a beginner in python and currently I am learning how lambda functions work. I want to know if there is a way for me to influence the output of a lambda + filter combo, because if I have understood how they work correctly, you can only return the element of the list you are iterating over, i.e., the argument of the lambda function. What I am exactly trying to achieve can be shown using a list comprehension
numbers = [25, 91, 22, -7, -20]
numbers_div_5_str = [str(n) for n in numbers if n % 5 == 0]
This gives a list of numbers in the form of a string that are divisible by 5. I want to achieve the same using lambda + filter, if possible
This is what I tried doing
numbers = [25, 91, 22, -7, -20]
numbers_div_5 = list(filter(lambda a : a % 5 == 0, numbers))
output -> [25, -20]
Expected output -> ['25', '-20']
In your example with a list comprehension you are doing two kinds of operations. 1) filtering elements from the original list with if n % 5 == 0 and 2) casting the values to be of type str with str(n).
Using the filter function can help you achieve your filtering (1) in exactly the way you tried already. The only thing remaining is to cast the values to str. Unfortunately you cannot just say str([1,2,3]) to transform all numbers in that list to be of type str. This has to be done element-wise. To achieve this you can use map. The syntax is roughly the same as filter, but this will take each element from your list and apply some kind of logic to it. This logic can be specified in a lambda function, or in this case you can simply use str on its own to cast your values.
here is an example in code
numbers = [25, 91, 22, -7, -20]
filtered_numbers = filter(lambda a : a % 5 == 0, numbers)
filtered_str_numbers = list(map(str, filtered_numbers))
Or more concise:
filtered_str_numbers = list(map(str, filter(lambda a : a % 5 == 0, numbers)))
Of course it's good to explore these functions and how they work for your knowledge, but in my experience it's totally fine to stick to list comprehensions in most cases.