Iterable Functions

There are many built-in functions in Python for processing iterables (such as list).

Some of them are:

• map
• filter
• all
• any
• reduce

map

Returns an object of map class which elements are modified according to the function.

The map class can be converted to some other collection with functions like:

• list() - to convert to list
• set() - to convert to a set, and so on.

def calculateSquare(n): return n * 2 numbers = [4, 8, 7, 6, 3]; multiplied_elements = map(calculateSquare, numbers) print(list(multiplied_elements))

Output:

[8, 16, 14, 12, 6]

filter

Returns an object of filter class which can be converted to other collection via list(), set() and other functions.

Allows filtering specific elements.

if the function returns true - the element will be present in the returned collection.

If the function returns false - it will not be present.

For example we can filter the list to return only the even numbers:

def check_even(number): return number % 2 == 0 numbers = [4, 8, 7, 6, 3] even_numbers = filter(check_even, numbers) print(list(even_numbers))

Output:

[4, 8, 6]

all

Returns a boolean. True - if all elements meet certain condition and False - if one or more elements don't meet the condition.

Let's look at the following example:

numbers = [4, 8, 7, 6, 3] only_even_numbers = [4, 8, 6] print(all(num % 2 == 0 for num in numbers)) print(all(num % 2 == 0 for num in only_even_numbers))

Output:

False True

any

Returns a boolean. True - if at least one of the elements meets certain condition and False - if all of the elements don't meet the condition.

Let's look at the following example:

oddNumbers = [3, 9, 7, 5]; mixedNumbers = [4, 1, 8]; print(any(num % 2 == 0 for num in oddNumbers)) print(any(num % 2 == 0 for num in mixedNumbers))

Output:

False True

reduce

The reduce function is part of the functools module and is used to accumulate a single value from the list.

It receives three arguments:

• A function which describes how to accumulate the end value through the iterations.
• iterable collection such as list
• initial value

Let's look at the following example:

from functools import reduce def custom_sum(total, value): print("Total: ", total) print("Value: ", value) print("- - - - - - - -") return total + value + 1 numbers = [3, 7, 2] # Using reduce to calculate custom sum sum = reduce(custom_sum, numbers, 5) print("End Sum: ", sum)

Output:

Total: 5 Value: 3 - - - - - - - - Total: 9 Value: 7 - - - - - - - - Total: 17 Value: 2 - - - - - - - - End Sum: 20

The following calculations are made until the end value - 20 is reached.

• The initial value starts with 5 (the third argument) - Total Value = 5.


• Total Value = Total Value + 3 + 1
• Total Value = 5 + 3 + 1 = 9


• Total Value = Total Value + 7 + 1
• Total Value = 9 + 7 + 1 = 17


• Total Value = Total Value + 2 + 1
• Total Value = 17 + 2 + 1 = 20