# FAQ: Functional Programming - Review of filter(), map(), and reduce()

This community-built FAQ covers the “Review of filter(), map(), and reduce()” exercise from the lesson “Functional Programming”.

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Hello!

I have found some mistakes in the lesson code snippets.

``````nums = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

# filter_values is not a higher-order function
def filter_values(predicate, lst):

# Mutable list required because this example is imperative, not declarative
ret = []
for i in lst:
if predicate(i):
ret.append(i)
return ret

filtered_numbers = filter_values(lambda x: x % 2 == 0, numbers)

print(k)

# This will output the tuple: (2, 4, 6, 8, 10)
``````

“nums” became “numbers” in the end;
“filetered_numbers” became “k” in the end;
“This will output the tuple” will not output the tuple, according to “return ret” statement (ret is a list).

``````nums = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

filtered_numbers = filter(lambda x: x % 2 == 0, numbers)

print(tuple(filtered_numbers))

# This will output the tuple: (2, 4, 6, 8, 10)
``````

“nums” became "numbers.

``````nums = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

def mapper(function, lst):
ret = []
for i in lst:
ret.append(function(i))
return ret

mapped_numbers  = mapper(lambda x: x*x, numbers)

print(tuple(k))

# This will output: (1, 4, 9, 16, 25, 36, 49, 64, 81, 100)
``````

“nums” became “numbers” in the end;
“mapped_numbers” became “k” in the end.

``````nums = (2, 6, 7, 9, 1, 4, 8)

sum = 0

for i in t:
sum += i

print(sum) # Output: 37
``````

“nums” became “t”

``````from functools import reduce

nums = (2, 6, 7, 9, 1, 4, 8)

k = reduce(lambda x, y: x + y, t) # k is a number

print(k) # Output: 37
``````

“nums” became “t”.

Hope this information will help somehow.

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