Data Collection and Processing with Python - Week 2 - 23.3 - Filter

23_3_Filter.py

# Now consider another common pattern: going through a list and keeping only those items that meet certain criteria. This is called a filter.

# Again, this pattern of computation is so common that Python offers a more compact and general way to do it, 
# the filter function. filter takes two arguments, a function and a sequence. The function takes one item
# and return True if the item should. It is automatically called for each item in the sequence. You don’t 
# have to initialize an accumulator or iterate with a for loop.

def keep_evens(nums):
    new_seq = filter(lambda num: num % 2 == 0, nums)
    return list(new_seq)

print(keep_evens([3, 4, 6, 7, 0, 1]))

# Output:
#[4, 6, 0]



# 1) Write code to assign to the variable filter_testing all the elements in lst_check that have a w in 
# them using filter.

lst_check = ['plums', 'watermelon', 'kiwi', 'strawberries', 'blueberries', 'peaches', 'apples', 'mangos', 'papaya']

filter_testing = filter(lambda word: "w" in word, lst_check)
print(filter_testing)

# Output: ['watermelon', 'kiwi', 'strawberries']



# 2. Using filter, filter lst so that it only contains words containing the letter “o”. Assign to
#  variable lst2. Do not hardcode this.

lst = ["witch", "halloween", "pumpkin", "cat", "candy", "wagon", "moon"]

lst2 = filter(lambda word: "o" in word, lst)
print(lst2)

# Output: ['halloween', 'wagon', 'moon']

lst = ["witch", "halloween", "pumpkin", "cat", "candy", "wagon", "moon"]
lst2 = list(filter(lambda have_o: 'o' in have_o , lst ))

lst_check = ['plums', 'watermelon', 'kiwi', 'strawberries', 'blueberries', 'peaches', 'apples', 'mangos', 'papaya']

filter_testing = list(filter(lambda have_w: 'w' in have_w , lst_check))