CODEWITHSUNDEEP
pythonlist
kate88
kate88

Reputation: 371

Adding counter/index to a list of lists in Python

I have a list of lists of strings:

listBefore = [['4', '5', '1', '1'],
              ['4', '6', '1', '1'],
              ['4', '7', '8', '1'],
              ['1', '2', '1', '1'],
              ['2', '3', '1', '1'],
              ['7', '8', '1', '1'],
              ['7', '9', '1', '1'],
              ['2', '4', '3', '1']]

and I would like to add a counter/index in the middle of each list so that the list looks like:

listAfter = [['4', '5', '1', '1', '1'],
             ['4', '6', '2', '1', '1'],
             ['4', '7', '3', '8', '1'],
             ['1', '2', '4', '1', '1'],
             ['2', '3', '5', '1', '1'],
             ['7', '8', '6', '1', '1'],
             ['7', '9', '7', '1', '1'],
             ['2', '4', '8', '3', '1']]

What would be the easiest way to do so? I could probably loop over the lists and add the index, but is there a cleaner way to do so?

Cheers, Kate

Edit: The code I wrote works for me:

item = 1
for list in listBefore:
    list.insert(2,str(item))
    item = item + 1
print listBefore

I was wondering if there is another way to do so more efficiently or in one step.

Upvotes: 1

Views: 705

Answers (4)

jamylak
jamylak

Reputation: 133764

>>> data = [['4', '5', '1', '1'],
            ['4', '6', '1', '1'],
            ['4', '7', '8', '1'],
            ['1', '2', '1', '1'],
            ['2', '3', '1', '1'],
            ['7', '8', '1', '1'],
            ['7', '9', '1', '1'],
            ['2', '4', '3', '1']]
>>> print [row[:len(row)//2] + [str(i)] + row[len(row)//2:]
           for i, row in enumerate(data, start=1)]
[['4', '5', '1', '1', '1'],
 ['4', '6', '2', '1', '1'],
 ['4', '7', '3', '8', '1'],
 ['1', '2', '4', '1', '1'],
 ['2', '3', '5', '1', '1'],
 ['7', '8', '6', '1', '1'],
 ['7', '9', '7', '1', '1'],
 ['2', '4', '8', '3', '1']]

Upvotes: 0

Moinuddin Quadri
Moinuddin Quadri

Reputation: 48120

Iterate over the parent list with enumerate() to get counter (used as i in the below example) along with list element. In the sublist, insert the i at the middle of sublist using list.insert(index, value) method. Note: The value of counter i.e. i will be of int type, so you have to explicitly type cast it to str as str(i)before inserting. Below is the sample code:

for i, sub_list in enumerate(my_list, 1):  # Here my_list is the list mentioned in question as 'listBefore'
    sub_list.insert(len(sub_list)/2, str(i))

# Value of 'my_list'
# [['4', '5', '1', '1', '1'], 
#  ['4', '6', '2', '1', '1'], 
#  ['4', '7', '3', '8', '1'],
#  ['1', '2', '4', '1', '1'], 
#  ['2', '3', '5', '1', '1'], 
#  ['7', '8', '6', '1', '1'], 
#  ['7', '9', '7', '1', '1'], 
#  ['2', '4', '8', '3', '1']]

Upvotes: 2

galfisher
galfisher

Reputation: 1122

You should learn about enumerate, it lets you iterate over the list with two iterators - one (str_list in this case) holds the current item in the list, and the other (i`) holds it's index in the list.

for i,str_list in enumerate(listBefore):
  listBefore[i] = str_list[:len(str_list)//2] + [str(i+1)] + str_list[len(str_list)//2:]

Upvotes: 0

Erik Godard
Erik Godard

Reputation: 6030

You can perform this with a list comprehension

listAfter = [listBefore[i][:len(listBefore[i])/2] + [str(i+1)] + listBefore[i][len(listBefore[i])/2:] for i in range(len(listBefore))]

Upvotes: 1

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