Issues with Lambda Function

[fad3r]

Hi,
I am trying to wrap my head around lambda but I am running into issues.

The homework question is: Write a lambda function that takes a list my_list and returns a list which includes only even numbers

my_list = [1, 5, 4, 6, 8, 11, 3, 12]
test = lambda my_list: my_list % 2 == 0


print test(my_list)

I feel like that should do it but I get an error when I try to run it. Not sure what is wrong with my logic.

[buran]

you need list comprehension in the lambda

[ThiefOfTime]

The Problem is that any numerical operand is only defined for values (int, double, long, etc.) not for lists.
the first solution that pops into my mind is:

my_list = [1,5,4,6,8,11,3,12]
test = lambda mylist: [el for el in mylist if el % 2 == 0]

print(test(my_list))

what you are doing is to get every element in the list, check if it is even and pack all even elements into a new list.
If the amount of elements becomes too high use numpy instead, there you can also use masks. But for small lists this would be a solution. but since you are constructing a new list you could use the list comprehension without the explizit function and lambda, but that depends on what you want to do with the lambda :)

[fad3r]

you need list comprehension in the lambda

The list comp does help but it returns boolean expression unless I did it wrong?

my_list = [1, 5, 4, 6, 8, 11, 3, 12]
test = lambda my_list: [my_list % 2 == 0 for my_list in my_list]


print (test(my_list))

[buran]

@ThiefOfTime already post the right solution
My code is the same

test = lambda my_list: [x for x in my_list if not x%2]

[fad3r]

The Problem is that any numerical operand is only defined for values (int, double, long, etc.) not for lists.
the first solution that pops into my mind is:

my_list = [1,5,4,6,8,11,3,12]
test = lambda mylist: [el for el in mylist if el % 2 == 0]

print(test(my_list))

what you are doing is to get every element in the list, check if it is even and pack all even elements into a new list.
If the amount of elements becomes too high use numpy instead, there you can also use masks. But for small lists this would be a solution. but since you are constructing a new list you could use the list comprehension without the explizit function and lambda, but that depends on what you want to do with the lambda :)

Yup this totally solves it. I have to spend some time to understand why yours works your way and mine at the bottom creates a boolean. The tip on the numerical operand piece was super helpful. I totally didnt know that.