Higher-order functions in Python and C#

In this article I will explain what is higher order function and how to implement it in programming languages like c# and python.

What is Higher Order Function(HOF):

so HOF is a function that either takes a function as an argument or returns a function. This type of function has implementations in many programming languages like javascript, python, Go, etc.

Some examples:

let's build very simple function called doOperation() which take a function as a first parameter and two numbers and will return a function that takes two numbers as an arguments,
we have also a function called sum() that returns summation of two numbers.

Python:

def doOperation(operation, num1, num2):
    return operation(num1, num2)

def sum(number1, number2):
    return number1 + number2

doOperation(sum, 2, 3)

-----------
Output: 5
-----------

Csharp

public int DoSomthing(Func<int,int,int> sum, int num1,int num2) =>
    sum(num1, num2);


public int sum(int number1, int number2) =>
    number1 + number2;


DoSomthing(sum, 2, 3)

----------------
Output: 5
----------------

in cshap example we use a built in delegate Func<int,int,int> which take 2 integer numbers and return integer to assign a sum function to it.

So with this implementation we already apply higher order function.

Another example

we want to create filter() function to filter an array based on function we can pass it for this filter() function.

Python:

def filter(arr, action):
   result= []
   for num in arr:
      if(action(num)):
         result.append(num)
   return result

def isOddNumber(num):
   return num % 2 != 0


filter([1, 2, 3, 4, 5], isOddNumber)

----------------
Output: [1,3,5]
----------------

Csharp

public static int[] Filter(int[] arr, Func<int, bool> func) =>
    arr.Where(func).OrderBy(n => n).ToArray();

public static bool isOddNumber(int number) =>
   number % 2 != 0;


Filter([1,2,3,4,5], isOddNumber)

------------------
Output: [1,3,5]
------------------