Find odd numbers in a list and square them using lambda function

Question

Here is the code I have got so far. Now output is [1, 3, 5, 7, 9]

N = 10
for i in range(1, 10):
    arr.append(i)

arr2 = []
f = lambda x: x ** 2
arr2 = filter(lambda x: x % 2 != 0, arr)
map(lambda x: x ** 2, arr2)
print(list(arr2))```

Asked By: Elgernon

||

Source

Answer 1

Here’s a very slightly modified version:

arr = []
N = 10
for i in range(1, N):
    arr.append(i)

arr2 = []
f = lambda x: x ** 2
arr2 = filter(lambda x: x % 2 != 0, arr)
for i in list(arr2):
    print(f(i))

arr2 isn’t a list. It’s an iterator, which you can only convert to a list once.

Here’s a more compact version:

N = 10
arr = range(1, N)

square = lambda x: x ** 2
keep_odd = lambda x: x % 2 != 0
arr2 = list(filter(keep_odd, arr))
for i in arr2:
    print(square(i))

print(arr2)

It outputs:

1
9
25
49
81
[1, 3, 5, 7, 9]

Answered By: Eric Duminil

Answer 2

You are discarding the result of f(i) as soon as you create it. You need to append it to some list (also, no need to consume the filter object into a list):

result = []
for i in arr2:
    result.append(f(i))

Please note that binding a lambda to an identifier is discouraged in accordance with PEP 8.

The best way to solve this problem is without list comprehensions is a combination of filter and map like so:

arr2 = list(map(lambda x: x ** 2, filter(lambda x: x % 2 != 0, arr)))

Answered By: iz_

Answer 3

You aren’t saving the value in the array, you are just printing it.

N = 10
for i in range(1, 10):
    arr.append(i)

result = []
f = lambda x: x ** 2
arr2 = filter(lambda x: x % 2 != 0, arr)
for i in arr2:
    result.append(f(i))    
print(result)

Answered By: Jonathan Porter

Answer 4

Your last for-loop applies the lambda function to the elements in your list, but does not save the result.
Try:

a = [i for i in range(1,10)]
a2 = filter(lambda x: x % 2 != 0, a)
a3 = map(lambda x: x**2, a2)        # This is a generator object
final_list = list(a3)               # This is a list

Python Tips on map filter reduce

Answered By: Kelym

Answer 5

lst = [1, 2, 3]

ans = list(map(lambda x: x ** 2, filter(lambda x: x % 2 != 0, lst)))

print(ans)

Answered By: Rakesh Kumar

Find odd numbers in a list and square them using lambda function

Question:

Answers: