Computer Science

# Lab 10 - Lists

## What does this print?

numbers = [1, 2, 3, 4, 5]
for number in numbers:
print(number)
def add_something(numbers, something):
result = []
for number in numbers:
result.append(number + something)
return result

def print_list(items):
for item in items:
print(item)

numbers = [2, 3, 4, 5]
print_list(numbers)
print_list(numbers)
def remove(numbers, target):
result = []
for number in numbers:
if number != target:
result.append(number)
return result

def print_list(items):
for item in items:
print(item)

numbers = [1, 2, 3, 1, 2, 3]
other = remove(numbers, 2)
print_list(other)
numbers = remove(numbers, 3)
print_list(numbers)

def geometric_mean(numbers):
total = 1
for number in numbers:
total = total * number

gm = geometric_mean([1, 2, 2, 4, 2])
print(gm)
gm = geometric_mean([3, 9, 1])
print(gm)

HINT:

$32^{\frac{1}{5}} = 2$

def as_ratios(numbers, factor):
result = []
for number in numbers:
result.append(number / factor)
return result

def floor(numbers, minimum):
result = []
for number in numbers:
if number < minimum:
number = minimum
result.append(number)
return result

def floor_ratios(numbers):
numbers = as_ratios(numbers, 100)
numbers = floor(numbers, 0.3)
for number in numbers:
print(number)

floor_ratios([5, 23, 55, 79])
def add(numbers, offset):
result = []
for number in numbers:
result.append(number + offset)
return result

def mod(numbers, factor):
result = []
for number in numbers:
result.append(number % factor)
return result

def find_min(numbers):
minval = None
for number in numbers:
if minval is None or number < minval:
minval = number
return minval

def mod_min(numbers, offset, factor):
numbers = mod(numbers, factor)
return find_min(numbers)

print(mod_min([1, 2, 3, 4], 3, 5))
print(mod_min([5, 7, 10, 22], 4, 6))

## Activities

For each of these activities, draw out your strategy. What are the series of steps you will take to solve each problem? How do those steps fit together?

### fun_with_lists.py

Implement the functions in fun_with_lists.py.

The tests are there to help you get started. What other tests could you write to make sure your implementations are correct?

### ceiling.py

Write a function ceiling(numbers, limit) that returns a copy of the list of numbers with each number greater than limit replaced with limit.

For example:

ceiling([1, 3, 5, 8], 4)

Would return:

[1, 3, 4, 4]

### sum_abs.py

Write a function sum_abs(numbers) that returns the sum of the absolute values of the numbers.

For example:

sum_abs([-2, 5, -8, 3])

Would return:

18

### average_positive.py

Write a function average_positive(numbers) that returns the average of the positive numbers in numbers.

For example:

average_positive([-2, 5, 7, -9, 3, -1])

Would return:

5.0

Break the problem into smaller pieces. What combination of simple patterns can you use to solve this problem? Write a function for each step.

### filter_infrequent.py

Write a function filter_infrequent(numbers, threshold) that returns a list of frequencies greater than the threshold.

The numbers are first converted to frequencies by dividing by the total (the sum of the numbers). Then frequencies less than threshold are removed.

Break the problem into smaller pieces. What combination of simple patterns can you use to solve this problem? Write a function for each step.

For example:

filter_infrequent([1, 2, 3, 4, 10], 0.1)

Would return;

[0.15, 0.2, 0.5]

What if you wanted filter_infrequent to return the original numbers instead of frequencies (but still filter out numbers that had a low corresponding frequency)?

### scale_to_unit.py

Write a function scale_to_unit(numbers) that returns the numbers translated and scaled to the unit scale (0 to 1).

This means that you must find the minimum value and subtract that from all numbers. Then find the maximum value of this new list and divide all of the numbers by this maximum.

For example:

scale_to_unit([1, 2, 3, 4, 5])

Would return:

[0, 0.25, 0.5, 0.75, 1]

fun_with_lists.py5 points
ceiling.py5 points
sum_abs.py5 points
average_positive.py5 points
filter_infrequent.py5 points
scale_to_unit.py5 points