Merge some list elements in a Python List by input Number

Question

I am having a hard time merging the elements within the Python list according to a given number.

I already found the solution to work on with a certain number. But I want to work with a variety of given number(N).

i.e. When I have a list

['There', 'was', 'a', 'farmer', 'who', 'had', 'a', 'dog', 'and', 'cat', '.']

Result,

When N = 2

['There was', 'a farmer', 'who had', 'a dog', 'and cat', '.']

or N = 3

['There was a', 'farmer who had', 'a dog and', 'cat .']

I would much prefer that it modified the existing list directly, not used any module or library.

Any help is greatly appreciated!!

Possible duplicate: https://stackoverflow.com/questions/434287/what-is-the-most-pythonic-way-to-iterate-over-a-list-in-chunks just `' '.join` the chunks — juanpa.arrivillaga, Apr 13 '19 at 16:42
"I would much prefer that it modified the existing list directly, not used any module or library." Why would you prefer those things? If you want to modify the list directly, it almost certainly will be inefficient. And why don't you want to use a module? — juanpa.arrivillaga, Apr 13 '19 at 16:42

score 0 · Accepted Answer · answered Apr 13 '19 at 16:47

Here's the sensible way to do it. it does create a new list. Since that is more efficient than trying to modify the original

a = ['There', 'was', 'a', 'farmer', 'who', 'had', 'a', 'dog', 'and', 'cat', '.']
n = 2
print([' '.join(a[i:i+n]) for i in range(0, len(a), n)])
n = 3
print([' '.join(a[i:i+n]) for i in range(0, len(a), n)])

Output:

['There was', 'a farmer', 'who had', 'a dog', 'and cat', '.']
['There was a', 'farmer who had', 'a dog and', 'cat .']

score 0 · Answer 2 · answered Apr 13 '19 at 16:48

0

This is the simplest way I can remember of:

my_list = ['a','b','c','d','e','f','g','h','i']
N = 3

my_list[0:N] = [''.join(my_list[0:N])]

answered Apr 13 '19 at 16:48

Miguel

1,295
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score 0 · Answer 3 · answered Apr 13 '19 at 17:10

    word_list = ['There', 'was', 'a', 'farmer', 'who', 'had', 'a', 'dog', 'and', 'cat', '.']
    new_word_list = []
    N = int(input())
    for i in range(0, len(word_list), N):
        string = ''
        for j in (range(len(word_list) - i) if len(word_list) - i < N else range(N)):
            string = string + word_list[i + j] + ' '
         new_word_list.append(string)

     print(new_word_list)

Here I implemented it using basic for loops to iterate over the list, although new list had to be created.

Merge some list elements in a Python List by input Number

3 Answers3