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Python program to concatenate every elements across lists

Last Updated : 30 Mar, 2023
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Given 2 lists, perform concatenations of all strings with each other across list.

Input : test_list1 = [“gfg”, “is”, “best”], test_list2 = [“love”, “CS”] 
Output : [‘gfg love’, ‘gfg CS’, ‘is love’, ‘is CS’, ‘best love’, ‘best CS’] 
Explanation : All strings are coupled with one another.

Input : test_list1 = [“gfg”, “best”], test_list2 = [“love”, “CS”] 
Output : [‘gfg love’, ‘gfg CS’, ‘best love’, ‘best CS’] 
Explanation : All strings are coupled with one another. 
 

Method #1: Using list comprehension

In this, we form pairs with each using list comprehension and then perform task of concatenation using another list comprehension.

Python3




# Python3 code to demonstrate working of
# All elements concatenation across lists
# Using list comprehension
 
# initializing lists
test_list1 = ["gfg", "is", "best"]
test_list2 = ["love", "CS"]
 
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
 
# forming pairs
temp = [(a, b) for a in test_list1 for b in test_list2]
 
# performing concatenation
res = [x + ' ' + y for (x, y) in temp]
 
# printing result
print("The paired combinations : " + str(res))
 






                        










Output:




The original list 1 is : [‘gfg’, ‘is’, ‘best’] The original list 2 is : [‘love’, ‘CS’] The paired combinations : [‘gfg love’, ‘gfg CS’, ‘is love’, ‘is CS’, ‘best love’, ‘best CS’]




Time Complexity: O(n2) -> two for loops


Space Complexity: O(n)


Method #2 : Using product() + list comprehension


In this, we perform task of forming combination using product() and list comprehension performs the task of concatenation.




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# Python3 code to demonstrate working of 


# All elements concatenation across lists


# Using product() + list comprehension


from itertools import product


 


# initializing lists


test_list1 = ["gfg", "is", "best"]


test_list2 = ["love", "CS"]


 


# printing original lists


print("The original list 1 is : " + str(test_list1))


print("The original list 2 is : " + str(test_list2))


 


# concatenation using formatting and pairing using product


res = ['%s %s' % (ele[0], ele[1]) for ele in product(test_list1, test_list2)]


 


# printing result 


print("The paired combinations : " + str(res))



















                        







                        










Output:




The original list 1 is : [‘gfg’, ‘is’, ‘best’] The original list 2 is : [‘love’, ‘CS’] The paired combinations : [‘gfg love’, ‘gfg CS’, ‘is love’, ‘is CS’, ‘best love’, ‘best CS’]




Time Complexity: O(n2) -> time complexity of product is O(n) and a for loop, O(n2)


Space Complexity: O(n)


Method #3: Using map and join


In this approach, we use map function to perform the task of concatenation and then join the resultant strings.




Python3














                                    




                                    

                                    




                                    




                                    

                                    

                                    
                                




















# Python3 code to demonstrate working of


# All elements concatenation across lists


# Using map() and join()


from itertools import product


# initializing lists


test_list1 = ["gfg", "is", "best"]


test_list2 = ["love", "CS"]


  


# printing original lists


print("The original list 1 is : " + str(test_list1))


print("The original list 2 is : " + str(test_list2))


  


# concatenation using map() and join()


res = list(map(' '.join, product(test_list1, test_list2)))


  


# printing result


print("The paired combinations : " + str(res))



















                        







                        










Output


The original list 1 is : ['gfg', 'is', 'best']
The original list 2 is : ['love', 'CS']
The paired combinations : ['gfg love', 'gfg CS', 'is love', 'is CS', 'best love', 'best CS']




Time Complexity: O(n2) -> time complexity of product is O(n) and a map function call O(n)


Auxiliary Space: O(n)


Method #4: Using itertools.product() and str.join()


    

  • Import the itertools module, which provides various functions to work with iterators.
    • 

  • Initialize two lists test_list1 and test_list2 with the desired elements.
    • 

  • Use itertools.product() function to form all possible pairs of elements from test_list1 and test_list2. This function returns an iterator that generates the pairs one at a time.
    • 

  • Store the iterator in a temporary variable called temp.
    • 

  • Iterate over the temp iterator and for each pair, join the elements using a space separator (‘ ‘) and append the result to a list called res.
    • 

  • Print the final result by converting the res list to a string using str() and passing it to the print() function
    • 





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import itertools


 


# initializing lists


test_list1 = ["gfg", "is", "best"]


test_list2 = ["love", "CS"]


 


# forming pairs


temp = itertools.product(test_list1, test_list2)


 


# performing concatenation


res = [' '.join(pair) for pair in temp]


 


# printing result 


print("The paired combinations : " + str(res))



















                        







                        










Output


The paired combinations : ['gfg love', 'gfg CS', 'is love', 'is CS', 'best love', 'best CS']





Time complexity: O(n^2), where n is the length of the longer list (since we form all possible pairs).
Auxiliary space: O(n^2) for the temp list, since we need to store all the pairs.




                                    


                                                                        

                                        

                                            

                                                

                                                    
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                                                    manjeet_04                                                

                                            

                                            

            
                                        

                                        

                                            
    

        
        
    
                                            

                                                
                                                
                                            

                                            

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