What is Lambda (Anonymous Function) in Python and How to use it with Filter, Map & Reduce

Anonymous function means that function which does not have a name, so now we can simply say function without having a name is lambda function. To create a normal function in python we need to use the def keyword and while creating the lambda function we need to use the lambda keyword. Hope you have got a brief idea of what is lambda in Python.

Normal Function:

Lambda Function:

Output:

 Output from normal function:  25 

 Output from lambda function:  25 

Here above-defined both function is returning the same thing but using lambda function we will be removing the uses of keywords like def, return and also we are reducing the number of lines, You can use any number of argument as you want but the expression should be only one. 

Lambda function does not require a return statement because it returns the expression itself directly. Where ever you need one expression with any number of arguments you can use the lambda function without even assigning the variable at all.

Use Lambda with Filter, Map & Reduce

Filter:

It is an inbuilt function in python, As the name suggests it takes the input (Iterable data) and returns the filtered data. Whenever you have a list or any other iterable and you want filtered data from that you can use the filter function it would be the best choice.

 filter(function, list) 

Now here you can see filter function takes two argument - list and function, List is your data that you want to filter, and function where you will define your operations. Here in the place of the function argument, we are going to use the lambda function. Now let's see in below code.

Using Filter with Lambda:

Output:

 Even numbers: [6, 12, 18] 

Explanation:

In the above example code, list_data is the list of any random integer and then I am passing it the to filter function. Now I have created the lambda function that will take list data one by one and match with our condition (even % 2 == 0) if the condition becomes is true then it will put the returned value inside a new list. And finally, we are printing the list i.e. even_num.

Map

It is an inbuilt function in python, It takes the input (Iterable data) and performs some operation as you define and returns final data. So if you want to perform some operation on all the elements of a list or any other iterable data you can use the map function.

 map(function, list) 

Now here you can see map function takes two arguments - list and function, List is your data that you want to perform some operation on it and function where you will define your operations. Here in the place of the function argument, we are going to use the lambda function. Now let's see in below code.

Using Map with Lambda:

Output:

 Double numbers: [6, 10, 18, 12, 26, 24, 36, 14] 

Explanation:

In the above example code, list_data is the list of any random integer and then I am passing it the to map function. Now I have created the lambda function that will take list data one by one and perform the operation (i.e. multiplying by 2) to each element of a list and then it will return the final list with having all the elements multiplied by 2.

Reduce

As the name suggests it will reduce your list to a single value. So if you have a chuck of value and you want to add all the values or multiply all the values you can choose this cool function to handle that for you.

 reduce(function, list) 

Now here you can see filter function takes two argument - list and function, List is your data that you want to reduce it into a single value and function where you will define your operations. Here in the place of the function argument, we are going to use the lambda function. 

Now here let me tell you one thing otherwise you will get an error while executing this code, reduce is not an inbuilt function it belongs to a module name as functools. Now from this module you can import reduce now let's see the example.

Using Reduce with Lambda:

Output:

 Addition result: 73 

Explanation:

In the above example code, list_data is the list of any random integer and then I am passing it the to map function. Now I have created the lambda function that will take list data and add all the elements one by one and then returns one single final value. 

If you see in this code you will not find a list while creating a reduce because reduce only returns a single value.

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