Table of contents

1. Explained in a nutshell
   1. Reference Document/video:
   2. map(): applies transforamtion to each element
   3. filter(): keeps only valid data after filtering
      1. lambda function on filter
   4. zip(): combining iterables

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Explained in a nutshell

• map(func, iterable) — transform each element
  • Input: a function and an iterable (list, tuple, etc.)
  • Logic: applies func to every element, one by one
  • Output: a map object (wrap with list() to see results)
  • Think of it as: “do this to every item”
• filter(func, iterable) — keep only matching elements
  • Input: a function that returns True/False + an iterable
  • Logic: keeps only elements where func(element) returns True
  • Output: a filter object (wrap with list() to see results), holding original elements that passed the filter
  • Think of it as: “only keep items that pass this test”
• zip(iter1, iter2, ...) — pair up elements across iterables
  • Input: two or more iterables of any type
  • Logic: pairs the nth element of each iterable into a tuple; stops at the shortest iterable
  • Output: a zip object of tuples (wrap with list() to see results)
  • Think of it as: “stitch these lists together side by side”

Reference Document/video:

• Linkedin Forum

map(): applies transforamtion to each element

    def square(x):
        return x ** 2
    numbers = [1, 2, 3, 4, 5]
    squared_numbers = list(map(square, numbers))

filter(): keeps only valid data after filtering

    def is_even(x):
        return x % 2 == 0
    numbers = [1, 2, 3, 4, 5]

    '''
    Think of : filter(is_even,numbers) --> temp "[False, True, False, True, False]" --> [2,4] 
    IMPORANT: The filter object DOES NOT HOLD the booleans, but holds the original elemnts that passed the filter
    '''

    even_numbers = list(filter(is_even, numbers))

lambda function on filter

zip(): combining iterables

    names = ['Alice', 'Bob', 'Charlie']
    ages = [25, 30, 35]
    combined = list(zip(names, ages))

• Another example with header list + elements nested list:

  •       headers = ['Name', 'Age', 'City']
          data = [['Alice', 25, 'New York'], ['Bob', 30, 'Los Angeles'], ['Charlie', 35, 'Chicago']]
          combined = list(zip(headers, *data))
    

  •       '''
          Quick reminder of *data
          * is the unpack operator
          * unpacks exactly one layer:
          '''
                                                
          data = [['Alice', 25, 'New York'], ['Bob', 30, 'Los Angeles'], ['Charlie', 35, 'Chicago']]
    
          *data  =  ['Alice', 25, 'New York'],  ['Bob', 30, 'Los Angeles'],  ['Charlie', 35, 'Chicago']
    

• Output would be:

    [('Name', 'Alice', 'Bob', 'Charlie'), ('Age', 25, 30, 35), ('City', 'New York', 'Los Angeles', 'Chicago')]