CSc 110

2D Lists

Benjamin Dicken

2D Lists!

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• We’ve used lists (1 dimensional lists) in this class so far
• Today:Use two-dimensional lists!
• The concepts discussed here can actually extend to N-dimensional lists, but I’ll mostly stick to 2D
• 2D lists useful for reading in CSV files manually

Review

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Should be familiar with this kind of list usage:

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items = [5, 10, 20, 6, 7, 8]

items[0] = 10

items[1] = 3

items[4] = 99

print(str(items))

2D list

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• To create a 2D list, we are, create a list-of-lists
• For example, this list

items = [[9, 8, 7, 8], [10, 20, 30, 4], [5, 50, 55, 4]]

• Can be represented by this diagram

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2D list

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items = [[9, 8, 7, 8],

[10, 20, 30, 4],

[5, 50, 55, 4]]

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• The “first dimension” is the outer list
• The “second dimension” are each of the inner lists
• When we draw pictures of 2D lists, the first dimension is the vertical axis, the second is the horizontal
• Notice how the list can be formatted to reflect the 2D diagram

2D list

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What will each of the below list accesses evaluate to?

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val_a = items[0][0]

val_b = items[2][3]

val_c = items[1][2]

print(val_a, val_b, val_c)

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items = [[9, 8, 7, 8],

[10, 20, 30, 4],

[5, 50, 55, 4]]

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Activity

Which lookups are valid?

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val_a = items[1][5] # ?

val_b = items[2][5] # ?

val_c = items[3][2] # ?

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items = [[9, 7, 8],

[1, 2, 3, 4, 5, 6],

[5],

[10, 20, 30]]

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Activity

Which lookups are valid?

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val_a = items[1][5] # OK

val_b = items[2][5] # NOT OK

val_c = items[3][2] # OK

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items = [[9, 7, 8],

[1, 2, 3, 4, 5, 6],

[5],

[10, 20, 30]]

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What will it print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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l1 = names[1][0][2]

l2 = names[2][1][2]

l3 = names[0][1][4]

print(l1 + l2 + l3)

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Activity

2D list

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names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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names ==

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names[2] ==

names[2][1] ==

names[2][1][0] ==

[["Ric", "Janet", "Joe"], ["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

["Cam", "Jan", "Jane"]

"Jan"

"J"

• 2D lists of strings are kind-of like a 3D list
• The first 2 dimensions are the lists, the last is the characters of the string

Traversing a 2d List

• As with regular lists, it is often useful to iterate (loop) through all of the elements in a 2D list
• This can be achieved in a few ways
• Using the indexes
• Using the actual values
• There are advantages to each one

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

print(i)

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Activity

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

print(i)

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['Ric', 'Janet', 'Joe']

['Ike', 'Alan', 'Ko']

['Cam', 'Jan', 'Jane']

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What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in names:

print(i)

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Activity

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in names:

print(i)

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['Ric', 'Janet', 'Joe']

['Ric', 'Janet', 'Joe']

['Ric', 'Janet', 'Joe']

['Ike', 'Alan', 'Ko']

['Ike', 'Alan', 'Ko']

['Ike', 'Alan', 'Ko']

['Cam', 'Jan', 'Jane']

['Cam', 'Jan', 'Jane']

['Cam', 'Jan', 'Jane']

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What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in names:

print(j)

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Activity

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in names:

print(j)

​

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['Ric', 'Janet', 'Joe']

['Ike', 'Alan', 'Ko']

['Cam', 'Jan', 'Jane']

['Ric', 'Janet', 'Joe']

['Ike', 'Alan', 'Ko']

['Cam', 'Jan', 'Jane']

['Ric', 'Janet', 'Joe']

['Ike', 'Alan', 'Ko']

['Cam', 'Jan', 'Jane']

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What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in i:

print(j)

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Activity

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in i:

print(j)

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Ric

Janet

Joe

Ike

Alan

Ko

Cam

Jan

Jane

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What would you change?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in i:

print(j)

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​

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Ric Janet Joe

Ike Alan Ko

Cam Jan Jane

Ric

Janet

Joe

Ike

Alan

Ko

Cam

Jan

Jane

Activity

What would you change?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in names:

for j in i:

print(j + '\t', end='')

print()

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Ric Janet Joe

Ike Alan Ko

Cam Jan Jane

Ric

Janet

Joe

Ike

Alan

Ko

Cam

Jan

Jane

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in range(0, len(names)):

for j in range(0, len(names[i])):

print(names[i][j], end="\t")

print()

Activity

What will this print?

names = [["Ric", "Janet", "Joe"],

["Ike", "Alan", "Ko"],

["Cam", "Jan", "Jane"]]

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for i in range(0, len(names)):

for j in range(0, len(names[i])):

print(names[-j-1][i], end="\t")

print()

Activity

CSV

• The CSV file format is a common way to represent tabular data
• Comma-Separated Values
• Regular text files, with particular rules about how the data within it is formatted
• Useful analogy: text representation of a excel spreadsheet

CSV Formatting

• Each line of the file representa a “row”
• Each line has value(s) separated by commas
• Each line should have the same number of columns
• The first line can (optionally) be a titles for each column

CSV Grades example

Name,SID,exam1,exam2,final

Steve,1429,67,84,91

Annie,3211,81,85,85

James,3171,90,75,80

Carlita,7877,85,87,89

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CSV Grades example (students.csv)

Name,SID,exam1,exam2,final

Steve,1429,67,84,91

Annie,3211,81,85,85

James,3171,90,75,80

Carlita,7877,85,87,89

Optional row of column titles

Each row represents a row of data (an entry in the student table

Each row has the same number of columns - to match the titles

CSV Grades example (students.csv)

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Steve,1429,67,84,91

Annie,3211,81,85,85

James,3171,90,75,80

Carlita,7877,85,87,89

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Title row is optional

Each row represents a row of data (an entry in the student table

Each row has the same number of columns - to match the titles

Load the contents of csv file into list

csv_data = []

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# What should go here?

1,4,7,2

3,10,20,30

3,4,7,1

1,1,1,2

1,5,5,1

0,1,0,1

numbers.csv

Activity

Load the contents of csv file into list

csv_data = []

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csv_file = open('numbers.csv', 'r')

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# What should go here?

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1,4,7,2

3,10,20,30

3,4,7,1

1,1,1,2

1,5,5,1

0,1,0,1

numbers.csv

Load the contents of csv file into list

csv_data = []

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csv_file = open('numbers.csv', 'r')

for line in csv_file:

line = line.strip('\n')

values = line.split(',')

# What should go here?

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​

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1,4,7,2

3,10,20,30

3,4,7,1

1,1,1,2

1,5,5,1

0,1,0,1

numbers.csv

Load the contents of csv file into list

csv_data = []

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csv_file = open('numbers.csv', 'r')

for line in csv_file:

line = line.strip('\n')

values = line.split(',')

csv_data.append(values)

​

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1,4,7,2

3,10,20,30

3,4,7,1

1,1,1,2

1,5,5,1

0,1,0,1

numbers.csv

Load the contents of csv file into list

csv_data = []

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csv_file = open('numbers.csv', 'r')

for line in csv_file:

line = line.strip('\n')

values = line.split(',')

csv_data.append(values)

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1,4,7,2

3,10,20,30

3,4,7,1

1,1,1,2

1,5,5,1

0,1,0,1

numbers.csv

What type are the values in the 2D list?

Activity

Load the contents of csv file into list

csv_data = []

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csv_file = open('numbers.csv', 'r')

for line in csv_file:

line = line.strip('\n')

values = line.split(',')

num_vals = []

for i in values:

num_vals.append( int(i) )

csv_data.append(num_vals)

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1,4,7,2

3,10,20,30

3,4,7,1

1,1,1,2

1,5,5,1

0,1,0,1

numbers.csv

Flip the order U/D

csv_data = []

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## Assume that the data has

## already been read in to

## csv_data

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# (1) First, flip the rows

# (2) Then, print them out

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1,4,7,2

1,5,5,1

0,1,0,1

numbers.csv

0 1 0 1

1 5 5 1

1 4 7 2

output

Activity

Flip the order U/D

csv_data = []

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flipped = []

for i in range(0, len(csv_data)):

ni = -1 - i

flipped.append( csv_data[ni] )

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# (2) Then, print them out

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1,4,7,2

1,5,5,1

0,1,0,1

numbers.csv

0 1 0 1

1 5 5 1

1 4 7 2

output

Flip the order U/D

csv_data = []

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flipped = []

for i in csv_data:

flipped.insert(0, i)

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# (2) Then, print them out

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1,4,7,2

1,5,5,1

0,1,0,1

numbers.csv

0 1 0 1

1 5 5 1

1 4 7 2

output

Flip the order U/D

csv_data = []

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flipped = []

for i in csv_data:

flipped.insert(0, i)

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for i in flipped:

for j in i:

print(str(j) + ' ', end='')

print()

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1,4,7,2

1,5,5,1

0,1,0,1

numbers.csv

0 1 0 1

1 5 5 1

1 4 7 2

output

Graphical Stock Plotter

Graphical Stock Plotter

red,apple,100,125,120,95,130,145,170,130,150,177,230,260

blue,exxon,60,67,72,81,80,72,68,64,64,70,72,68

green,toyota,20,27,17,32,50,58,67,82,85,90,99,105

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stocks.csv

Graphical Stock Plotter

red,apple,100,125,120,95,130,145,170,130,150,177,230,260

blue,exxon,60,67,72,81,80,72,68,64,64,70,72,68

green,toyota,20,27,17,32,50,58,67,82,85,90,99,105

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stocks.csv

* Download plot.py

* Implement main

Activity

from graphics import graphics

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def get_stock_data():

f = open('stocks.csv', 'r')

data = []

for line in f:

row = []

sp = line.split(',')

row.append(sp[0])

row.append(sp[1])

for element in sp[2:]:

row.append(int(element))

data.append(row)

return data

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def main():

stock_data = get_stock_data()

gui = graphics(600, 300, 'stocks')

i = 0

while i < len(stock_data):

print(stock_data[i])

color = stock_data[i][0]

# TODO: Draw the label

j= 0

while j < len(stock_data[i])-2:

x = 10 + (j*50)

y = -(stock_data[i][j+2]-300)

# TODO: Draw the line

# TODO: Draw the dot

j += 1

i += 1

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main()

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from graphics import graphics

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def get_stock_data():

f = open('stocks.csv', 'r')

data = []

for line in f:

row = []

sp = line.split(',')

row.append(sp[0])

row.append(sp[1])

for element in sp[2:]:

row.append(int(element))

data.append(row)

return data

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def main():

stock_data = get_stock_data()

gui = graphics(600, 300, 'stocks')

i = 0

while i < len(stock_data):

print(stock_data[i])

color = stock_data[i][0]

gui.text(5, 5+30*i, stock_data[i][1], color, 25)

j= 0

prev_x = -1

prev_y = -1

while j < len(stock_data[i])-2:

x = 10 + (j*50)

y = -(stock_data[i][j+2]-300)

if prev_x >= 0:

gui.line(prev_x, prev_y, x, y, color, 2)

gui.ellipse(x, y, 10, 10, color)

prev_x = x

prev_y = y

j += 1

i += 1

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main()

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