2D Lists

Jake Shoudy

Sept 28, 2022

CSCI 110 - Lecture 17

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HW6

Lists!

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Due Friday (9/30) at 11:59pm

Lab6

Posted yesterday morning!

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More lists practice!

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Attempt before Friday at 11:59pm to count as Participation/Attendance for the week

Quiz 5 Scores

Recap

Review: Style Guide

What is it?

Standard in which programmers write code

Why is it important?

Makes code easy to read and organized

Everyone follows same standard, so when work together, know code will look a certain way

Python Style Guide

Variable and function names: all lowercase with underscores between words

Expressions and functions: exactly one space on either side of operator, parentheses only where necessary, no extra spaces

Review: Lists

What?

Data structure containing ordered list of elements, which can be strings, numbers, other data types, and other data structures including lists

Is a data type, just like str, int, bool, float

Can len(), index, slice, in, iterate, replace item, concat (using +)

List functions: append, extend, insert, remove, pop

Why?

Hold data that needs to stay in a certain order

Review: Mutability

ages = [3, 5, 8, 9]

ages.append(7)

ages = ages + [3, 4, 11]

ages.remove(3)

ages.insert(1, 10)

ages[2] = 12

ages.pop(1)

ages.extend([8, 2])

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[3, 5, 8, 9, 7]

[3, 5, 8, 9, 7, 3, 4, 11]

[5, 8, 9, 7, 3, 4, 11]

[5, 10, 8, 9, 7, 3, 4, 11]

[5, 10, 12, 9, 7, 3, 4, 11]

[5, 12, 9, 7, 3, 4, 11]

[5, 12, 9, 7, 3, 4, 11, 8, 2]

Lists: Getting Items vs Mutability

states = []

states.append("AL")

states.insert(len(states), "CA")

states.extend(["NY", "TN"])

states.pop()

states.remove("CA")

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states = ["AL", "NY", "TN", "CA"]

states[0]

states[1:3]

len(states)

states[1:2] + states[3:]

"CA" in states

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2D Lists

Adding to lists

companies = []

companies.extend(['Google', 'Facebook'])

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companies.extend(['Apple', 'Amazon', 'Zillow'])

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companies.append(['Microsoft', 'Lyft'])

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['Google', 'Facebook']

['Google', 'Facebook', 'Apple', 'Amazon', 'Zillow']

['Google', 'Facebook', 'Apple', 'Amazon', 'Zillow', ['Microsoft', 'Lyft']]

Accessing our list

companies =� ['Google', 'Facebook', 'Apple', 'Amazon', 'Zillow', ['Microsoft', 'Lyft']]

companies[5]

['Microsoft', 'Lyft']

companies[6]

IndexError

companies[5][0]

'Microsoft'

companies[5][1]

'Lyft'

companies[5][2]

IndexError

companies[5][1][2]

'f'

2D (2-dimensional) Lists

A 2D list is a list of lists!

Ex: my_2d_list = [['a', 'b', 'c'], ['x', 'y', 'z']]

Can access inner list by indexing

Ex: my_2d_list[0] -> ['a', 'b', 'c']

Can access inner list values by indexing that list

Ex: my_2d_list[0][1] -> 'b'

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What can we do with 2D lists?

Represent grids!

Lists of "outer" list each represents one row

Each value in "inner" lists represents value for a column

What can we do with 2D lists?

Candy Crush!

How to keep track of which symbol is in each cell of grid?

2D List: Candy Crush

[

['blue', 'red', 'yellow', 'blue'],

['purple', 'fish', 'yellow', 'yellow'],

['wall', 'orange', 'red', 'yellow']

]

Databases

Databases

database: collection of organized information to be easily accessed, managed, and/or updated

Internet Movie Database (IMDb)

Database Records

Database Records

one record

Database Records

fields

Database Records as Nested Lists

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

2D List: Indexing

Just like for lists, can index into 2D lists

All list functions work for 2D lists, because 2D lists are lists!

To index: first index “outer” list, then index into resulting “inner” list

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2D Lists: Indexing

song = songs[3]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

2D Lists: Indexing

song = songs[3]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

2D Lists: Indexing

song = songs[3][0]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

2D Lists: Indexing

song = songs[0][3]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

2D Lists: Indexing

song = songs[4][2]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

2D Lists: Indexing

song = songs[5][2]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

IndexError!

2D Lists: Indexing

song = songs[1][4]

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

0

1

2

3

4

IndexError!

2D List: Iterating

Just like for lists, can iterate over 2D lists

2D Lists: Iterating

songs = [

['Circles', 'Post Malone', 2019, 'Psychedelic Pop'],

['Ransom', 'Lil Tecca', 2019, 'Hip Hop/Rap'],

['BOP', 'DaBaby', 2019, 'Hip Hop/Rap'],

['Truth Hurts', 'Lizzo', 2019, 'Pop'],

['223\'s (feat. 9lokknine)', 'YNW Melly', 2019, 'Hip Hop/Rap'],

]

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for song in songs:

print('Song: ' + song[0])

print('Artist: ' + song[1])

print('Year: ' + str(song[2]))

print('Genre: ' + song[3])

print()

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Let’s Code!

https://replit.com/team/csci110-01

2D Lists

2D Lists

What?

List of lists

Can use all list functions on 2D lists because they are lists

Can index and iterate through 2D lists to access stored data

Why?

Holds data in particular order in which each item has many elements

databases: collection of organized information to be easily accessed, managed, and/or updated

Questions?