IBM Data Engineer Professional Certificate - Coursera

gistfile1.txt

Lists in Python
Estimated time needed: 15 minutes

Objectives
After completing this lab you will be able to:

Perform list operations in Python, including indexing, list manipulation, and copy/clone list.
Table of Contents
About the Dataset
Lists
Indexing
List Content
List Operations
Copy and Clone List
Quiz on Lists
About the Dataset
Imagine you received album recommendations from your friends and compiled all of the recommandations into a table, with specific information about each album.

The table has one row for each movie and several columns:

artist - Name of the artist
album - Name of the album
released_year - Year the album was released
length_min_sec - Length of the album (hours,minutes,seconds)
genre - Genre of the album
music_recording_sales_millions - Music recording sales (millions in USD) on SONG://DATABASE
claimed_sales_millions - Album's claimed sales (millions in USD) on SONG://DATABASE
date_released - Date on which the album was released
soundtrack - Indicates if the album is the movie soundtrack (Y) or (N)
rating_of_friends - Indicates the rating from your friends from 1 to 10


The dataset can be seen below:

Artist	Album	Released	Length	Genre	Music recording sales (millions)	Claimed sales (millions)	Released	Soundtrack	Rating (friends)
Michael Jackson	Thriller	1982	00:42:19	Pop, rock, R&B	46	65	30-Nov-82		10.0
AC/DC	Back in Black	1980	00:42:11	Hard rock	26.1	50	25-Jul-80		8.5
Pink Floyd	The Dark Side of the Moon	1973	00:42:49	Progressive rock	24.2	45	01-Mar-73		9.5
Whitney Houston	The Bodyguard	1992	00:57:44	Soundtrack/R&B, soul, pop	26.1	50	25-Jul-80	Y	7.0
Meat Loaf	Bat Out of Hell	1977	00:46:33	Hard rock, progressive rock	20.6	43	21-Oct-77		7.0
Eagles	Their Greatest Hits (1971-1975)	1976	00:43:08	Rock, soft rock, folk rock	32.2	42	17-Feb-76		9.5
Bee Gees	Saturday Night Fever	1977	1:15:54	Disco	20.6	40	15-Nov-77	Y	9.0
Fleetwood Mac	Rumours	1977	00:40:01	Soft rock	27.9	40	04-Feb-77		9.5
Lists
Indexing
We are going to take a look at lists in Python. A list is a sequenced collection of different objects such as integers, strings, and even other lists as well. The address of each element within a list is called an index. An index is used to access and refer to items within a list.

Image
To create a list, type the list within square brackets [ ], with your content inside the parenthesis and separated by commas. Let’s try it!

# Create a list
​
L = ["Michael Jackson", 10.1, 1982]
L = ['Mark Lising', 8.2, 1967]
We can use negative and regular indexing with a list:

Image
# Print the elements on each index
​
print('the same element using negative and positive indexing:\n Postive:',L[0],
'\n Negative:' , L[-3]  )
print('the same element using negative and positive indexing:\n Postive:',L[1],
'\n Negative:' , L[-2]  )
print('the same element using negative and positive indexing:\n Postive:',L[2],
'\n Negative:' , L[-1]  )
the same element using negative and positive indexing:
 Postive: Mark Lising 
 Negative: Mark Lising
the same element using negative and positive indexing:
 Postive: 8.2 
 Negative: 8.2
the same element using negative and positive indexing:
 Postive: 1967 
 Negative: 1967
List Content
Lists can contain strings, floats, and integers. We can nest other lists, and we can also nest tuples and other data structures. The same indexing conventions apply for nesting:

# Sample List
​
["Michael Jackson", 10.1, 1982, [1, 2], ("A", 1)]
['Michael Jackson', 10.1, 1982, [1, 2], ('A', 1)]
List Operations
We can also perform slicing in lists. For example, if we want the last two elements, we use the following command:

# Sample List
​
L = ["Michael Jackson", 10.1,1982,"MJ",1]
L = L[3:5]
Image
# List slicing
​
L[3:5]
[]
We can use the method extend to add new elements to the list:

(['dancer', 'actor'])
# Use extend to add elements to list
​
L = [ "Michael Jackson", 10.2]
L.extend(['pop', 10])
L.extend(['dancer', 'actor'])
Another similar method is append. If we apply append instead of extend, we add one element to the list:

.append(['dancer', 'actor'])
# Use append to add elements to list
​
L = [ "Michael Jackson", 10.2]
L.append(['pop', 10])
L.append(['dancer', 'actor'])
Each time we apply a method, the list changes. If we apply extend we add two new elements to the list. The list L is then modified by adding two new elements:

ext
# Use extend to add elements to list
​
L = [ "Michael Jackson", 10.2]
L.extend(['pop', 10])
L.extend(['dancer', 'actor'])
If we append the list ['a','b'] we have one new element consisting of a nested list:

# Use append to add elements to list
​
L.append(['a','b'])
L.append(['c','d'])
As lists are mutable, we can change them. For example, we can change the first element as follows:

# Change the element based on the index
​
A = ["disco", 10, 1.2]
print('Before change:', A)
A[0] = 'hard rock'
print('After change:', A)
Before change: ['disco', 10, 1.2]
After change: ['hard rock', 10, 1.2]
We can also delete an element of a list using the del command:

# Delete the element based on the index
​
print('Before change:', A)
del(A[0])
print('After change:', A)
Before change: ['hard rock', 10, 1.2]
After change: [10, 1.2]
We can convert a string to a list using split. For example, the method split translates every group of characters separated by a space into an element in a list:

# Split the string, default is by space
​
'hard rock'.split()
['hard', 'rock']
We can use the split function to separate strings on a specific character which we call a delimiter. We pass the character we would like to split on into the argument, which in this case is a comma. The result is a list, and each element corresponds to a set of characters that have been separated by a comma:

# Split the string by comma
​
'A,B,C,D'.split(',')
['A', 'B', 'C', 'D']
Copy and Clone List
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When we set one variable B equal to A, both A and B are referencing the same list in memory:

# Copy (copy by reference) the list A
​
A = ["hard rock", 10, 1.2]
B = A
print('A:', A)
print('B:', B)
A: ['hard rock', 10, 1.2]
B: ['hard rock', 10, 1.2]
Image
Initially, the value of the first element in B is set as "hard rock". If we change the first element in A to "banana", we get an unexpected side effect. As A and B are referencing the same list, if we change list A, then list B also changes. If we check the first element of B we get "banana" instead of "hard rock":

# Examine the copy by reference
​
print('B[0]:', B[0])
A[0] = "banana"
print('B[0]:', B[0])
B[0]: hard rock
B[0]: banana
This is demonstrated in the following figure:

Image
You can clone list A by using the following syntax:

# Clone (clone by value) the list A
​
B = A[:]
B
['banana', 10, 1.2]
Variable B references a new copy or clone of the original list. This is demonstrated in the following figure:

Image
Now if you change A, B will not change:

print('B[0]:', B[0])
A[0] = "hard rock"
print('B[0]:', B[0])
B[0]: banana
B[0]: banana
Quiz on List
Create a list a_list, with the following elements 1, hello, [1,2,3] and True.

# Write your code below and press Shift+Enter to execute
my_list=[1, 'hello', [1, 2, 3], True]
Click here for the solution
a_list = [1, 'hello', [1, 2, 3] , True]
a_list
Find the value stored at index 1 of a_list.

my_list[1]
# Write your code below and press Shift+Enter to execute
my_list[1]
'hello'
Click here for the solution
a_list[1]
Retrieve the elements stored at index 1, 2 and 3 of a_list.

# Write your code below and press Shift+Enter to execute
my_list[1:4]
['hello', [1, 2, 3], True]
Click here for the solution
a_list[1:4]
Concatenate the following lists A = [1, 'a'] and B = [2, 1, 'd']:

A+B
# Write your code below and press Shift+Enter to execute
A+B
['hard rock', 10, 1.2, 'banana', 10, 1.2]
Click here for the solution
A = [1, 'a'] 
B = [2, 1, 'd']
A + B