Concept of Map vs List Comprehension in Python

Suppose you want to execute a code where you want to define a function in a single line to make your code look simpler in that case you can use List Comprehension or Map() function and you can use it in many parts of your code. The topic like Map vs List comprehension in python is much common and equally important that any python developer will come across. The difference in the implementation of these function and methods and the concept behind is what need to understand and will explain through my views

Map() function in Python-

Map() function executes each item in an iterates way present in list, tuple, set, etc. The respective items passed as a parameter to the map function present in the list.

List Comprehension in Python-

  1. The list comprehension is a replacement of for loop.

Example:

You define a list –

list=[2,3,4,6,7]

But you need to define list  of longer range  like(0,100):

list=[]
 for i in range(0,1000):
   list.append()

This code will give the output elements in the range like 0,1,… 999.

But using list comprehension the code will look clear.

list=[i for i in range(0,1000)]

 

This list implementation will give the same output, but this methodology is much simpler, and time- saving and easy to debug.

The list is an alternate way of using for lambda in the map(), filter() and reduce() because the use of map or filter function needs to write the number of lines while use list comprehension we can implement the same operation within one line.

It is considered to be Pythonic, due to its simplicity, code is easy to understand.

 

Syntax of Map() function:

 

variable=map(function-name,iterable)

Function-name-The function which is needed to be executed.

Iterable-The value in the list or tuple that is automatically iterated calculating along with the function.

 

EXAMPLE:

def square(num):   #declaring the function
   return num**2    #return the function output


In the above code, you define the function with the respective argument ‘num’ and returning the argument value.

list=[2,3,5,7,8] # declaring & defining the list

Then you define the list, or you can use a tuple or also a set over here.

x=map(square,list)

Here we use the map function to map the respective function & list used in the code and with the help of map function. It iterates each element of the defined list to give the output in the form of their square value.

 

Here you print the list and you get the element of the list in their square value.

 

print(x) #print the value of x print
print(list(x)) # print x in form of list 




OUTPUT- 
[4,9,25,49,64] 
[4,9,25,49,64]

The lambda function is also implemented along with map function to generate the new list as output.

 

num_list = [5, 7, 6,8] 
final_list = list(map(lambda x: x**2 , num_list)

Here you can see I have to define num_list and with the help of map and lambda function, I tried to map the element to give their square value as output as a new list.

But this approach makes the code look complicated.

print(final_list)

OUTPUT-
[25,49,36,64]

This is the following output of the above code.

Syntax of  List comprehension:

list=[expression for element in iterable]

Expression-variable use for each element to iterate.

Element-items on the list.

 

EXAMPLE-

list = [2, 3, 4, 6, 7,8] 

Here you define the respective list.

  
x = [i * 3 for i in list ]

Here in the above code a variable “i” is used to iterate the items in the list that get store in the variable “x”.

print(x)


OUTPUT-
[8,27,64,216,343,512]

 

 

The print function gives the output of x which the cube root value of elements in the defined list. The list comprehension method is easier to implement, saves time, a single line of code can make the code look more clear and easy to debug.

Pros and cons of list comprehension:

  1. List comprehension method is fast-

The list comprehension method is easier to implement due to the single line of its expression. Its time saving mostly when you are engaged to debug a big code that time you can implement list comprehension method to make the code look consistent, rather than implementing map() or for loop() where you have to define function then iterate it by mapping elements of the list with it or using loop where you have created an empty list and append element accordingly as it iterates to the condition given.

  1. It is a concise way to generate a list along with the implement the loop and respective operation rather than creating a list then performing loop or using functions.
  2. It looks easier to understand than map function., due to its simplicity in its definition.
  3. It is a more approachable way to expresses the list to define and it is content at the same time rather than creating an empty list and putting element at the end.

Pros and Cons of Map function:

  1. It is slower than the list comprehension method. Map faster in terms of calling the function that is already defined in the code.
  2. The map function is more time consuming to implement like writing several lines makes code more complicated to understand whereas using list comprehension you can implement it just one list just time-saving and easy to debug.

Also read: List and dictionary comprehension in python

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