nested_list_notes_finished.py

"""
Name: Mr. C
Title: 2D lists and nested loops notes 
Description: Introduces Two-dimensional lists (lists within lists) and nested for loops. This program continues to use the idea of a row of cars to represent a list.
"""

"""
  What are 2D lists or nested lists?
    A 2D list is a two-dimensional list, or a list containing other lists or sequences. Think of it like a matrix with rows and columns, or in the case of a row of cars, a parking lot of rows and spaces. e.g.:
      
            col1    col2    col3    col4
    row1    ford    toyota  buick   gm
    row2    nissan  lexus   jeep    ford
    row3    bmw     honda   toyota  gm
    row4    tesla   bmw     jeep    toyota
    
    The more general term is a nested sequence (applies to tuples as well).
"""

#1 Creating a 2D list (i.e. our parking lot of cars)
lot = [
	["ford", "toyota", "buick", "gm"], 		# row 1 ( index 0 )
    ["nissan", "lexus", "jeep", "ford"],	# row 2
    ["bmw", "honda", "toyota", "gm"],		# row 3
    ["tesla", "bmw", "jeep", "toyota"]		# row 4
]

print(lot)

if "ford" in lot[0]:  # True for a row, lot[0]
	print(True)
else:				  # False for lot
	print(False)

#2 Accessing a nested list (i.e. a row of cars)
print("\nThe first row of cars...")
print(lot[0])
print("\nAll rows of cars...")
for row in lot:
	print(row)

#3 Accessing an individual element from a 2D list (i.e. a car)

print("\nThe first car in the lot...")
print(lot[0][0])

# On your own: display each of the following...
print("\nThe 1st car in row 4:", end="") 
print(lot[3][0])

print("\nThe 2nd car in row 2:", end="") 
print(lot[1][1])

print("\nAll cars in the 3rd column:") 
for row in lot:
	print(row[2])
	
print("\nAll cars in the 4th row with a tab inbetween them:")
for car in lot[3]:
	print(car, end="\t\t")


print("\nTry changing the first ford to an audi and then display it: ")
print(lot[0])
lot[0][0] = "audi"
print(lot[0])

input("\nPress Enter to Continue...")

# Using nested for loops to display the individual elements in row / column format
print("\nPrint the lot in row / column format...")
for row in lot:  # nested loop
	for car in row:
		print(f"{car}     ", end="\t\t")
	print()

print("\nAccessing the index values for the lot...")
#for row in range(4):
for row in range(len(lot)):  # best way
	#for col in range(4):
	#for col in range(len(lot[0])):
	for col in range(len(lot[row])):  # best way
		print(row, col, end="\t\t")
	print()

input("\nPress Enter to Continue...")

#4 Unpacking a sequence - assigning each element of a sequence its own variable in a single line of code.

# Another nested list example: 
a_row = [
	["Ford", "Fusion"], 
	["Audi", "A4"], 
	["BMW", "3 Series"],
	["Jeep", "Wrangler"]
] 

print(a_row)

for car in a_row:
	#print(car[0], car[1])
	make, model = car  # unpacking a sequence
	print(make, model)

#5 Appending a new sequence
make = input("Enter a new make: ")
model = input("Enter a new model: ")
car = [make, model]

print(a_row)
a_row.append(car)
print(a_row)

#6 Sorting a 2D list
print("\nRow of cars sorted by make:")
print(a_row)
a_row.sort()
print(a_row)

#7 Sorting a 2D list by elements other than the first
#  We have a new module that we need to use... operator (and the itemgetter function).
print("\nRow of cars sorted by model:")
from operator import itemgetter
a_row.sort(key=itemgetter(1))
print(a_row)

#8 Reverse
print("\nRow of cars reverse sorted by model:") 
a_row.sort(key=itemgetter(1), reverse=True)
print(a_row)

#9 Searching in and the break keyword
#   You have to loop through to find if an indvidual element is in a nested sequence

a_row.insert(0, ["BMW", "4 series"])

for car in a_row:
	if "BMW" in car:
		print("Found a BMW.")
		break # will break out of a for or while loop
	else:
		print("Not a BMW").