Module 05. Collections and Iteration
Lecture Date 1: September 20, 2021 - Monday Slides-1
Lecture Date 2: September 22, 2021 - Wednesday Slides-2
DataCamp Chapters: Introduction to Python -> Python Lists
Intermediate Python -> Dictionaries and Pandas
Intermediate Python -> Loops
So far, we have learned about variables that can hold a value. In this lecture, we will learn special variable types (or objects to be correct) that can hold multiple values. Imagine, you would like to model the motion of masses and want to store all the trajectory points, it will be very difficult if you don’t use a collection like list which is the first part of this lecture. Simultaneously, if you want to work on lists, it is challenging to do so without using a concept called iteration, or loops. Loops allow the programmer to iterate through collections like lists. Loops will be the second topic of this lecture. Apart from lists, we will study three other collections types, namely tuples, dictionaries, and sets. We will cover when to use which collection with code examples. Once you master in lists and loops, you can build think about building cool models such as the one presented in the following video.
Table of contents:
1. Lists
1.1. Creating lists
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
mixed_list = [1, "Banana", True, 1.0 ]
list_within_list = [1, 5, 10, ["one", "two", "three"], 25 ]
1.2. Accesing list elements
cities[0]
'Fairfax'
cities[4]
'Vienna'
cities[7]
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-6-ca6e618667fa> in <module>
----> 1 cities[7]
IndexError: list index out of range
print(cities[-1], cities[-4])
Centreville Herndon
print(cities[-8])
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-8-da8bc98ca84a> in <module>
----> 1 print(cities[-8])
IndexError: list index out of range
cities[1:4]
['Alexandria', 'Reston', 'Herndon']
list_within_list[3][0]
'one'
1.3. List Functions
new_list=[]
new_list.append(3.14)
new_list
[3.14]
new_list.append(-999.14)
new_list
[3.14, -999.14]
new_list.append(True)
new_list
[3.14, -999.14, True]
new_list.extend([5,6,7,5])
new_list
[3.14, -999.14, True, 5, 6, 7, 5]
new_list.insert(0, "Hello")
new_list
['Hello', 3.14, -999.14, True, 5, 6, 7, 5]
new_list.insert(4, "World")
new_list
['Hello', 3.14, -999.14, True, 'World', 5, 6, 7, 5]
new_list.insert(-1, ["inner","list"])
new_list
['Hello', 3.14, -999.14, True, 'World', 5, 6, 7, ['inner', 'list'], 5]
print(new_list.index(3.14))
1
print(new_list.pop())
5
new_list
['Hello', 3.14, -999.14, True, 'World', 5, 6, 7, ['inner', 'list']]
new_list.remove(["inner","list"])
new_list
['Hello', 3.14, -999.14, True, 'World', 5, 6, 7]
new_list.sort()
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-31-fa91de0f3b3b> in <module>
----> 1 new_list.sort()
TypeError: '<' not supported between instances of 'float' and 'str'
print(new_list.count(5))
1
1.4. Collection functions
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
number_of_cities = len(cities)
print(number_of_cities)
7
print("Vienna" in cities)
print("Arlington" in cities)
True
False
2. Tuples, Dictionaries, and Sets
2.1. Tuples
cities_tuple = ("Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville")
print(cities_tuple)
('Fairfax', 'Alexandria', 'Reston', 'Herndon', 'Vienna', 'Oakton', 'Centreville')
cities_tuple2 = "Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"
print(cities_tuple2)
('Fairfax', 'Alexandria', 'Reston', 'Herndon', 'Vienna', 'Oakton', 'Centreville')
Tuple packing
val1, val2, val3 = 100, 200, 300
print(val1, val2, val3)
100 200 300
val2, val1 = val1, val2
print(val1, val2, val3)
200 100 300
2.2. Sets
cities_set = {"Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"}
print(cities_set)
{'Fairfax', 'Vienna', 'Oakton', 'Centreville', 'Alexandria', 'Herndon', 'Reston'}
cities_set2 = set(["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"])
print(cities_set2)
{'Fairfax', 'Vienna', 'Oakton', 'Centreville', 'Alexandria', 'Herndon', 'Reston'}
set2 = set([1,4,5,1,1,5,7,1,7,1,6,4,5,7,1])
print(set2)
{1, 4, 5, 6, 7}
set1 = set([1,2,3])
set2 = set([2,3,4])
print(set1.union(set2))
{1, 2, 3, 4}
2.3. Dictionary
dct = { }
dct[0] = 'some data'
dct[5] = [5, 'more data']
dct['astring'] = (4,5)
dct[(5,6)] = 'a point'
list(dct.keys())
[0, 5, 'astring', (5, 6)]
list(dct.values())
['some data', [5, 'more data'], (4, 5), 'a point']
# print keys before popping
print(list(dct.keys()))
# next line will remove the dictionary item w/ key=5
value = dct.pop(5)
print(f'Removed item value: {value}')
# print keys after popping
print(list(dct.keys()))
[0, 5, 'astring', (5, 6)]
Removed item value: [5, 'more data']
[0, 'astring', (5, 6)]
2.4. Collection functions
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
number_of_cities = len(cities)
print(number_of_cities)
7
print("Vienna" in cities)
print("Arlington" in cities)
True
False
3. Loops
Download code
Imagine that you are asked to simulate the projection of a free falling object every 0.1 seconds.
y1=50 # initial position
vy=0 # initial velocity
g=9.8 # gravity
t=0.0
new_position = y1+vy*t-0.5*g*t**2
print(f"At time={t}, the position of the object is at {new_position}")
t=0.1
new_position = y1+vy*t-0.5*g*t**2
print(f"At time={t}, the position of the object is at {new_position}")
t=0.2
new_position = y1+vy*t-0.5*g*t**2
print(f"At time={t}, the position of the object is at {new_position}")
t=0.3
new_position = y1+vy*t-0.5*g*t**2
print(f"At time={t}, the position of the object is at {new_position}")
At time=0.0, the position of the object is at 50.0
At time=0.1, the position of the object is at 49.951
At time=0.2, the position of the object is at 49.804
At time=0.3, the position of the object is at 49.559
3.1. The for loop
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
for city in cities:
print(city)
Fairfax
Alexandria
Reston
Herndon
Vienna
Oakton
Centreville
for letter in "GMU":
print(letter)
G
M
U
coordinates = [(0,0), (0.4, 0.1), (0.7, 0.2), (0.99, 0.3)]
for coor in coordinates:
print("x,y: ",coor)
x,y: (0, 0)
x,y: (0.4, 0.1)
x,y: (0.7, 0.2)
x,y: (0.99, 0.3)
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
for city in cities:
for letter in city:
print(letter,end=".")
print()
F.a.i.r.f.a.x.
A.l.e.x.a.n.d.r.i.a.
R.e.s.t.o.n.
H.e.r.n.d.o.n.
V.i.e.n.n.a.
O.a.k.t.o.n.
C.e.n.t.r.e.v.i.l.l.e.
3.2. Range
for num in range(9, 0, -2):
print(num)
9
7
5
3
1
for num in range(5):
print(num*num)
0
1
4
9
16
3.3. Enumerate
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
for index in range(len(cities)):
print(index+1,".",cities[index])
1 . Fairfax
2 . Alexandria
3 . Reston
4 . Herndon
5 . Vienna
6 . Oakton
7 . Centreville
for index, city in enumerate(cities):
print(index+1,".",city)
1 . Fairfax
2 . Alexandria
3 . Reston
4 . Herndon
5 . Vienna
6 . Oakton
7 . Centreville
3.4. Zip
indexes = [1, 2, 3, 4, 5, 6, 7]
cities = ["Fairfax", "Alexandria", "Reston", "Herndon", "Vienna", "Oakton", "Centreville"]
for item in zip(indexes, cities):
print(item)
(1, 'Fairfax')
(2, 'Alexandria')
(3, 'Reston')
(4, 'Herndon')
(5, 'Vienna')
(6, 'Oakton')
(7, 'Centreville')
for item in zip(indexes, cities):
print(item[0],".",item[1])
1 . Fairfax
2 . Alexandria
3 . Reston
4 . Herndon
5 . Vienna
6 . Oakton
7 . Centreville
list1 = [0,1,2]
list2 = ["zero", "one", "two"]
list3 = ["cero", "uno", "dos"]
for item in zip(list1, list2, list3):
print(item)
(0, 'zero', 'cero')
(1, 'one', 'uno')
(2, 'two', 'dos')
list1 = [0,1,2]
list2 = ["zero", "one", "two", "three"]
for item in zip(list1, list2):
print(item)
(0, 'zero')
(1, 'one')
(2, 'two')
list1 = [0,1,2, 3]
list2 = ["zero", "one", "two"]
for item in zip(list1, list2):
print(item)
(0, 'zero')
(1, 'one')
(2, 'two')
3.5. The while loop
index = 0
while index < 5:
index = index + 1 # or index+= 1
print(index)
1
2
3
4
5
list2 = ["zero", "one", "two"]
index = 0
while index < len(list2):
print(list2[index])
index+= 1
zero
one
two
3.6 Control Flow
for num in range(11):
if num % 2 == 0:
print(num, "is an even number.")
else:
print(num, "is an odd number.")
0 is an even number.
1 is an odd number.
2 is an even number.
3 is an odd number.
4 is an even number.
5 is an odd number.
6 is an even number.
7 is an odd number.
8 is an even number.
9 is an odd number.
10 is an even number.
num = 0
max_number = 5
while True:
if num > max_number:
break
if num % 2 == 0:
print(num, "is an even number.")
else:
print(num, "is an odd number.")
num += 1
0 is an even number.
1 is an odd number.
2 is an even number.
3 is an odd number.
4 is an even number.
5 is an odd number.
for num in range(11):
if num % 2 == 0:
continue
print(num, "is an odd number.")
1 is an odd number.
3 is an odd number.
5 is an odd number.
7 is an odd number.
9 is an odd number.
first_list = ["Hello", "World", 2000, True]
empyt_tuple = tuple()
one_elem_list = list([True])
print( any(first_list))
print( all(first_list))
print( any(empyt_tuple))
print( all(empyt_tuple))
print( any(one_elem_list))
print( all(one_elem_list))
True
True
False
True
True
True
3.7. Example
Three ways of generating numbers from 0.0 to 3.0 with .1 increments
time = []
for i in range(31):
time.append(i/10.0)
print (time)
[0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0]
time = []
i = 0
while i <= 30:
time.append(i/10)
i += 1
print (time)
[0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0]
time = [i/10 for i in range(31)]
print(time)
[0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0]
3.8. Print example (see slides)
num_of_character = 10
charachter_to_print = "*"
for i in range(num_of_character):
print(end=charachter_to_print)
**********
num_of_character = 20
charachter_to_print = "-"
counter=0
while counter < num_of_character:
print(end=charachter_to_print)
counter = counter + 1
--------------------
3.9. Dropping example (see slides)
starting_height = 100
initial_velocity = 0
gravity = -9.8
pos_list = [starting_height]
for i in range(1,46):
t = i / 10
y2 = starting_height + initial_velocity*t + 0.5 * gravity * t ** 2
pos_list.append(y2)
#print(“time:“,t, ” height:“, y2)
print("-----------")
print("Positions")
print(pos_list)
distance_list = []
for i in range(len(pos_list)-1):
distance_list.append(pos_list[i]-pos_list[i+1])
print("-----------")
print("Distances")
print (distance_list)
-----------
Positions
[100, 99.951, 99.804, 99.559, 99.216, 98.775, 98.236, 97.599, 96.864, 96.031, 95.1, 94.071, 92.944, 91.719, 90.396, 88.975, 87.45599999999999, 85.839, 84.124, 82.311, 80.4, 78.39099999999999, 76.28399999999999, 74.07900000000001, 71.776, 69.375, 66.876, 64.279, 61.584, 58.791, 55.9, 52.91099999999999, 49.823999999999984, 46.639, 43.356, 39.974999999999994, 36.49599999999999, 32.91899999999998, 29.244, 25.471000000000004, 21.599999999999994, 17.631, 13.563999999999993, 9.399000000000001, 5.1359999999999815, 0.7749999999999915]
-----------
Distances
[0.049000000000006594, 0.14699999999999136, 0.24500000000000455, 0.3430000000000035, 0.4409999999999883, 0.5390000000000015, 0.6370000000000005, 0.7349999999999994, 0.8329999999999984, 0.9310000000000116, 1.0289999999999964, 1.1269999999999953, 1.2250000000000085, 1.3229999999999933, 1.4210000000000065, 1.5190000000000055, 1.6169999999999902, 1.7150000000000034, 1.8129999999999882, 1.9110000000000014, 2.0090000000000146, 2.1069999999999993, 2.204999999999984, 2.3030000000000115, 2.4009999999999962, 2.4989999999999952, 2.5970000000000084, 2.694999999999993, 2.7930000000000064, 2.8909999999999982, 2.9890000000000114, 3.0870000000000033, 3.184999999999981, 3.2830000000000013, 3.3810000000000073, 3.4790000000000063, 3.5770000000000053, 3.674999999999983, 3.772999999999996, 3.8710000000000093, 3.968999999999994, 4.067000000000007, 4.164999999999992, 4.263000000000019, 4.36099999999999]