lambdas_collections.txt

#### Lambdas
In Python, a lambda function is a single-line function declared with no name, which can have any number of arguments, but it can only have one expression.
is a function without a name (you can also call it an anonymous function)

# An example is a square function:

# this is equivalent
def square(num):
    return num * num

# to the lambda
square_lambda = lambda num : num * num

# this is called like this:
assert square(3) == square_lambda(3)

two = lambda: 2
sqr = lambda x: x * x
pwr = lambda x, y: x ** y

for a in range(-2, 3):
    print(sqr(a), end=" ")
    print(pwr(a, two()))

##### 
# Processing a collection with 'map':
# Let's assume we have a list of integers and we want to get another list
# where all the elements are multiplied by 2. We can use the 'map' function
# for this:
domain = [1, 2, 3, 4, 5]
our_range = map(lambda num: num * 2, domain)
print(list(our_range)) # we need to convert to list here, as map returns a 
                       # a map object
# this will return:
[2, 4, 6, 8, 10]
##
# Processing a collection with 'filter':
domain = [1, 2, 3, 4, 5]
our_range = map(lambda num: num * 2, domain)
print(list(our_range))

evens = filter(lambda num: num % 2 == 0, domain)
print(list(evens))
# If we run this (we get the evens):
[2, 4, 6, 8, 10]
[2, 4]

# Sort using the key parameter. It takes a function that each item in the 
# collection will be processed with before the comparison is run to determine
# the order.

# For example:
words = ['Boss', 'a', 'Alfred', 'fig', 'Daemon', 'dig']
print("Sorting by default")
print(sorted(words))
# we get:
['Alfred', 'Boss', 'Daemon', 'a', 'dig', 'fig']

print("Sorting with a lambda key")
print(sorted(words, key=lambda s: s.lower()))
# we get:
['a', 'Alfred', 'Boss', 'Daemon', 'dig', 'fig']
####