How to merge two nested lists and output a list of lists of tuples?

Question

I have two nested lists, list_a and list_b :

list_a=[['a','b'],['c','d','e'],['f','g','f']]
list_b=[[5,7],[2,3,2],[4,7,8]]

I am trying to produce list_c which would be the result of merging each element in list_a with its corresponding element in list_b eg list_a[1][1] with list_b[1][1] and list_a[1][2] with list_b[1][2] , etc. to produce a list of lists of tuples.

list_c=[[('a',5),('b',7)],[('c',2),('d',3),('e',2)],[('f',4),('g',7),('f',8)]]

I had already tried:

list_c=[]
for list1 in list_a:
    for list2 in list_b:
        list_c.append(list(zip(list1,list2)))

But the output for this is a list of lists of tuples of all possible combinations of the elements in the original lists:

[[('a', 5), ('b', 7)], [('a', 2), ('b', 3)], 
 [('a', 4), ('b', 7)], [('c', 5), ('d', 7)],...
 [('f', 2), ('g', 3), ('f', 2)], 
 [('f', 4), ('g', 7), ('f', 8)]]

I feel like I'm close to the right answer, but am missing something simple. How do I produce a list_c of the structure I am looking for? (Preserving the order matters, since I'd like to use this for working on a CSV file)

This is an extension to the question asked here: Concatenate items in two nested lists to pairs in tuples

But I've been unable to find any similar questions that don't involve flattening the resulting list into something like:

list_c=[('a',5),('b',7),('c',2),('d',3),('e',2),('f',4),('g',7),('f',8)]

Answer 1

You need to zip over list_a and list_b , not do a nested for-loop (a product): something to the effect of:

[list(zip(a,b)) for a,b in zip(list_a, list_b)]

In other words:

result = []
for a, b in zip(list_a, list_b):
    result.append(list(zip(a,b)))

Answer 2

using list comprehension

a=[['a','b'],['c','d','e'],['f','g','f']]
b=[[5,7],[2,3,2],[4,7,8]]

c = [list(zip(i,j)) for i,j in zip(a,b)]

print(c)

"""
output 


[[('a', 5), ('b', 7)],
 [('c', 2), ('d', 3), ('e', 2)],
 [('f', 4), ('g', 7), ('f', 8)]]

"""

using lambda function this can be done as

d=list(map(lambda x,y:list(zip(x,y)),a,b))
print(d) 
"""
output 

[[('a', 5), ('b', 7)],
 [('c', 2), ('d', 3), ('e', 2)],
 [('f', 4), ('g', 7), ('f', 8)]]

"""

Answer 3

list_c = []
for i, element_a in enumerate(list_a):
    element_b = list_b[i]
    merged_list = []
    for j in range(len(element_a)):
        merged_list.append((element_a[j], element_b[j]))
    list_c.append(merged_list)

Create new tuple for each element in each list index and append to master list

Answer 4

Since the best and shorter method is already taken.., another option with the good old verbose for loop:

list_c = []
for i, a in enumerate(list_a):
  tmp = []
  for j, b in enumerate(list_b[i]):
    tmp.append((a[j], b))
  list_c.append(tmp)

list_c
#=> [[('a', 5), ('b', 7)], [('c', 2), ('d', 3), ('e', 2)], [('f', 4), ('g', 7), ('f', 8)]]