Day26

Day 26: Map, Filter, and Zip

Instructions:

1. Open a new python file.
2. Calculate the area based on a list of radii. The area() function is created to do the calculation and then a for loop is used to transform the items in the list.

   import math
   
   def area(r: float) -> float:
       """
       Calculate the area of a circle based on the radius.
       :param r: The radius of the circle: Float
       :return: The area of the circle: Float
       """
       return math.pi * (r ** 2)
   
   radii = [4, 5, 123, 42, 12.5]
   
   areas = []
   for rad in radii:
       a = area(rad)
       areas.append(a)
   
   print(areas)
   

3. This entire process can be completed in a single line of code using map() and lambdas. The map() function creates a map object, so in order to produce the final list output, the list() function is required. The map() function has two required inputs: map(function, iterative object).

   import math
   radii = [4, 5, 123, 42, 12.5]
   areas = list(map(lambda r: math.pi * (r ** 2), radii))
   print(areas)
   print(map(lambda r: math.pi * (r ** 2), radii))
   

4. The filter() function is similar to the map() function where a function is applied to each item in the iterable object. However, filter() is used to only return items that return the True response. Additionally, the filter() function creates a filter object, so the list() function is required to store the output in a list. In order to understand why lambda i: i % 2 provides a list of odd values, execute print(int(True)).

   # Filter all even values out of a list.
   odds = list(filter(lambda i: i % 2, range(100)))
   print(odds)
   print(filter(lambda i: i % 2, range(100)))
   

5. The zip() function is used to create an iterable object of tuples. While this function can be done using map(), it is a native way to create a list of tuples by joining multiple lists. Similar to compressing a folder into a .zip file, the zip() function compresses multiple iterable objects into a single object. The output of the zip() function is a zip object. Therefore, the output from the zip() function can be saved as a list with the list() function.

   sb_num = ['I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII', 'IX', 'X', 'XI', 'XII', 'XIII', 'XIV', 'XV', 'XVI', 'XVII',
             'XVIII', 'XIX', 'XX', 'XXI', 'XXII', 'XXIII', 'XXIV', 'XXV', 'XXVI', 'XXVII', 'XXVIII', 'XXIX', 'XXX', 'XXXI',
             'XXXII', 'XXXIII', 'XXXIV', 'XXXV', 'XXXVI', 'XXXVII', 'XXXVIII', 'XXXIX', 'XL', 'XLI', 'XLII', 'XLIII',
             'XLIV', 'XLV', 'XLVI', 'XLVII', 'XLVIII', 'XLIX', '50', 'LI', 'LII', 'LIII']
   
   sb_date = ['Jan. 15, 1967', 'Jan. 14, 1968', 'Jan. 12, 1969', 'Jan. 11, 1970', 'Jan. 17, 1971', 'Jan. 16, 1972',
              'Jan. 14, 1973', 'Jan. 13, 1974', 'Jan. 12, 1975', 'Jan. 18, 1976', 'Jan. 9, 1977', 'Jan. 15, 1978',
              'Jan. 21, 1979', 'Jan. 20, 1980', 'Jan. 25, 1981', 'Jan. 24, 1982', 'Jan. 30, 1983', 'Jan. 22, 1984',
              'Jan. 20, 1985', 'Jan. 26, 1986', 'Jan. 25, 1987', 'Jan. 31, 1988', 'Jan. 22, 1989', 'Jan. 28, 1990',
              'Jan. 27, 1991', 'Jan. 26, 1992', 'Jan. 31, 1993', 'Jan. 30, 1994', 'Jan. 29, 1995', 'Jan. 28, 1996',
              'Jan. 26, 1997', 'Jan. 25, 1998', 'Jan. 31, 1999', 'Jan. 30, 2000', 'Jan. 28, 2001', 'Feb. 3, 2002',
              'Jan. 26, 2003', 'Feb. 1, 2004', 'Feb. 6, 2005', 'Feb. 5, 2006', 'Feb. 4, 2007', 'Feb. 3, 2008',
              'Feb. 1, 2009', 'Feb. 7, 2010', 'Feb. 6, 2011', 'Feb. 5, 2012', 'Feb. 3, 2013', 'Feb. 2, 2014',
              'Feb. 1, 2015', 'Feb. 7, 2016', 'Feb. 5, 2017', 'Feb. 4, 2018', 'Feb. 3, 2019']
   
   sb_winners = ['Green Bay', 'Green Bay', 'New York Jets', 'Kansas City', 'Baltimore', 'Dallas', 'Miami', 'Miami',
                 'Pittsburgh', 'Pittsburgh', 'Oakland', 'Dallas', 'Pittsburgh', 'Pittsburgh', 'Oakland', 'San Francisco',
                 'Washington', 'Los Angeles Raiders', 'San Francisco', 'Chicago', 'New York Giants', 'Washington',
                 'San Francisco', 'San Francisco', 'New York Giants', 'Washington', 'Dallas', 'Dallas', 'San Francisco',
                 'Dallas', 'Green Bay', 'Denver', 'Denver', 'St. Louis', 'Baltimore', 'New England', 'Tampa Bay',
                 'New England', 'New England', 'Pittsburgh', 'Indianapolis', 'New York Giants', 'Pittsburgh',
                 'New Orleans', 'Green Bay', 'New York Giants', 'Baltimore', 'Seattle', 'New England', 'Denver',
                 'New England', 'Philadelphia', 'New England']
   
   sb_losers = ['Kansas City', 'Oakland', 'Baltimore', 'Minnesota', 'Dallas', 'Miami', 'Washington', 'Minnesota',
                'Minnesota', 'Dallas', 'Minnesota', 'Denver', 'Dallas', 'Los Angeles Rams', 'Philadelphia', 'Cincinnati',
                'Miami', 'Washington', 'Miami', 'New England', 'Denver', 'Denver', 'Cincinnati', 'Denver', 'Buffalo',
                'Buffalo', 'Buffalo', 'Buffalo', 'San Diego', 'Pittsburgh', 'New England', 'Green Bay', 'Atlanta',
                'Tennessee', 'New York Giants', 'St. Louis', 'Oakland', 'Carolina', 'Philadelphia', 'Seattle', 'Chicago',
                'New England', 'Arizona', 'Indianapolis', 'Pittsburgh', 'New England', 'San Francisco', 'Denver',
                'Seattle', 'Carolina', 'Atlanta', 'New England', 'Los Angeles Rams']
   
   sb_score = [(35, 10), (33, 14), (16, 7), (23, 7), (16, 13), (24, 3), (14, 7), (24, 7), (16, 6), (21, 17), (32, 14),
               (27, 10), (35, 31), (31, 19), (27, 10), (26, 21), (27, 17), (38, 9), (38, 16), (46, 10), (39, 20), (42, 10),
               (20, 16), (55, 10), (20, 19), (37, 24), (52, 17), (30, 13), (49, 26), (27, 17), (35, 21), (31, 24),
               (34, 19), (23, 16), (34, 7), (20, 17), (48, 21), (32, 29), (24, 21), (21, 10), (29, 17), (17, 14), (27, 23),
               (31, 17), (31, 25), (21, 17), (34, 31), (43, 8), (28, 24), (24, 10), (34, 28), (41, 33), (13, 3)]
   
   super_bowl = list(zip(sb_num, sb_date, sb_winners, sb_losers, sb_score))
   print(super_bowl)
   

6. The reduce() function will not be discussed since BDFL is quoted saying, "So now reduce(). This is actually the one I've always hated most, because, apart from a few examples involving + or *, almost every time I see a reduce() call with a non-trivial function argument, I need to grab pen and paper to diagram what's actually being fed into that function before I understand what the reduce() is supposed to do. So in my mind, the applicability of reduce() is pretty much limited to associative operators, and in all other cases it's better to write out the accumulation loop explicitly."
7. Update the log file with what you have learned today.