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

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

list = [['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:

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

I know the for loop is correct because the following code produces true six times.

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

CodePudding user response：

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

CodePudding user response：

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.