Is it possible to use .join() to concatenate a list of strings in a nested list in Python?

Question

I’m trying to use join() in a nested list with an if statement. If the condition is met, I want to combine all indices from [1:-3]. Every time the join() function doesn’t join the index.

Input

a = [['a', 'b', 'c', 'd'], ['a', 'b', 'c', 'd', 'e','f','g'], ['a', 'b', 'c', 'd']]

Expected Output

[['a', 'b', 'c', 'd'], ['a', 'b c d', 'e','f','g'], ['a', 'b', 'c', 'd']]

What I have tried:

a = [' '.join(str(inner_list)) for inner_list in a for i in inner_list if len(inner_list) >= 6 ]

I know the for loop is correct because the following code produces true for a[1][0] and iterates through a[][]. To my understanding, the loop is iterating over the correct part but won’t join() from the index [1][1] to [1][3]. This is where I’m very confused.

the index

a = [print("true") for inner_list in a for i in inner_list if len(inner_list) >= 6 ]

Asked By: SkyLearning

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Source

Answer 1

for inner_list in list_:
   for i in inner_list:
      if len(inner_list) >= 6:
         print("".join((inner_list)))

output:

a b c d e f g
a b c d e f g
a b c d e f g
a b c d e f g
a b c d e f g
a b c d e f g
a b c d e f g

i converted it to what it actually does , just i did not put it inside a list.
if you could specify the output you are looking for. Also
in your code you should remove str(inner_list) as i think it is not doing what you intend it to do.

please share intended output too , so i answer better.

your code updated

list = [['a', 'b', 'c', 'd'], ['a', 'b', 'c', 'd', 'e','f','g'], ['a', 'b', 'c', 'd']]

list = [' '.join((inner_list)) for inner_list in list for i in inner_list if len(inner_list) >= 6 ]

output list :

['a b c d e f g',
 'a b c d e f g',
 'a b c d e f g',
 'a b c d e f g',
 'a b c d e f g',
 'a b c d e f g',
 'a b c d e f g']

Upon if you want to use that [1:-3] indexing too

list = [['a', 'b', 'c', 'd'], ['a', 'b', 'c', 'd', 'e','f','g'], ['a', 'b', 'c', 'd']]

list = [' '.join((inner_list[1:-3])) for inner_list in list for i in inner_list if len(inner_list) >= 6 ]

output list :

['b c d',
 'b c d',
 'b c d',
 'b c d',
 'b c d',
 'b c d',
 'b c d']

ps : also try not to use default keywords as variable names like list

Answered By: BOTMAN

Answer 2

You need to slice the inner lists in the loop, but also pass the remaining inner lists as they are if they’re smaller than 6 items. Here’s an example:

lst = [['a', 'b', 'c', 'd'], ['a', 'b', 'c', 'd', 'e', 'f', 'g'], ['a', 'b', 'c', 'd']]

new_lst = [[l[0:1] + [' '.join(l[1:-3])] + l[-3:]] if len(l) >= 6 else l for l in lst]
print(new_lst)

# Output
# [['a', 'b', 'c', 'd'], [['a', 'b c d', 'e', 'f', 'g']], ['a', 'b', 'c', 'd']]

join() takes a list as an argument instead of a string, and also try to refrain from using built in types like list as variable names.

Answered By: LTJ

Is it possible to use .join() to concatenate a list of strings in a nested list in Python?

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