Lists Patterns¶

🖌 Transforming a List¶

transform_a_list.py¶

This demonstrates the mapping pattern.

Map is a mathematical term that means going from one value to a corresponding value.

This is also referred to as the transform pattern.

👨🏼‍🎨 smaller_numbers.py¶

Write a function that creates a new list where each item has been divided by 2.

You can pass lists to functions and return lists from functions.

🖌 Filtering Lists¶

only_odds.py¶

This demonstrates the filter pattern.

A new collection is created with certain items filtered out.

NOTES

  • Step through with debugger
  • Show how numbers are added only if they are odd

🖌 Selecting from a List¶

find_min.py¶

This demonstrates the selection pattern.

A single item is selected from a collection.

NOTES

  • is None: this is how you check if a variable points to None
  • Step through in debugger
  • Look at logic of if condition
    • See how the value of smallest updates only sometimes

🖌 Accumulation¶

average.py¶

This demonstrates the accumulator pattern.

total accumulates the values in the collection.

NOTES

  • Step through in debugger
  • Show how total updates

👩🏻‍🎨 All Together¶

Given a list of numbers, write a function that substracts 7 and removes the negative numbers or numbers greater than 10.

all_together.py¶

Another way for list patterns¶

In [28]:
numbers = [1, 2, 3, 4, 5]

sum¶

In [29]:
sum(numbers)
Out[29]:
15
In [30]:
sum(numbers) / len(numbers)
Out[30]:
3.0

List comprehensions¶

Mapping pattern¶

In [32]:
new_numbers = []
for number in numbers:
    new_number = number + 7
    new_numbers.append(new_number)
new_numbers
Out[32]:
[8, 9, 10, 11, 12]
In [33]:
[number + 7 for number in numbers]
Out[33]:
[8, 9, 10, 11, 12]
In [34]:
[number / 3 for number in numbers]
Out[34]:
[0.3333333333333333,
 0.6666666666666666,
 1.0,
 1.3333333333333333,
 1.6666666666666667]
In [36]:
[number ** 2 for number in numbers]
Out[36]:
[1, 4, 9, 16, 25]
In [37]:
[number ** 0.5 for number in numbers]
Out[37]:
[1.0, 1.4142135623730951, 1.7320508075688772, 2.0, 2.23606797749979]

Filter pattern¶

In [38]:
new_numbers = []
for number in numbers:
    if number > 3:
        new_numbers.append(number)
new_numbers
Out[38]:
[4, 5]
In [39]:
[number for number in numbers if number > 3]
Out[39]:
[4, 5]
In [40]:
[number for number in numbers if number % 2 == 0]
Out[40]:
[2, 4]
In [42]:
[number for number in numbers if number * 5 < 20]
Out[42]:
[1, 2, 3]

All Together with comprehensions¶

In [43]:
nums = [0, 7, 2, 14, 20, 32, 5, 12]

# subtract 7
nums = [number - 7 for number in nums]

# Keep 0 <= num <= 10
def is_keeper(number):
    return 0 <= number <= 10

nums = [number for number in nums if is_keeper(number)]

print(nums)

[0, 7, 5]

Key Ideas¶

  • mapping pattern
  • filter pattern
  • selection pattern
  • accumulator pattern
  • List comprehensions
    • mapping pattern
    • filter pattern