CODEWITHSUNDEEP
python-2.7
Barry Keegan
Barry Keegan

Reputation: 81

Combine lines and convert to list

Example Lines from txt file:

one
two
three
one1
two2
three3

Desired result:

['one', 'two', 'three']

['one1', 'two2', 'three3']

How can I combine every 3 lines into 1 and convert to list?

I would like this to continue through a large text file with hundreds of lines.

This code I took from another thread bu it only combines 2 per line

f = open('joining-lines-template.txt')

mod_list = []
count = 1
for line in f:
    line = line.rstrip()
    if count % 2 == 0:
        mod_list.append(old_line+line)
    else:
        old_line = line
    count += 1
print(mod_list)

CLARIFICATION

The final output when printed should look like below, with lists on new lines rather than all on the one line.

['one', 'two', 'three']

['one1', 'two2', 'three3']

Upvotes: 0

Views: 752

Answers (1)

Jean-François Fabre
Jean-François Fabre

Reputation: 140168

I would read the file fully, then create a list comprehension with slicing 3 by 3:

with open("input.txt") as f:
   lines = list(f)   # convert file to list of lines so slicing works
   result = [lines[i:i+3] for i in range(0,len(lines),3) ]

Variant: here's a way which doesn't need to read all the file at once:

with open("input.txt") as f:
    result = [[l,next(f),next(f)] for l in f]

But saving memory has a price:

  • It's a little "hacky" because it uses the iteration of the loop for the first item, but forces iterations for the 2 next items
  • If the file has not a number of lines divisible by 3 then it will fail

beginners may like a full "classical" python code:

result = []
sublist = []
for l in f:
    sublist.append(l)
    if len(sublist)==3:
        result.append(sublist)
        sublist = []

if sublist:
    result.append(sublist)

in all cases to print the list of lists as you need just to:

for l in result:
    print(l)  # prints the representation of the sublist

Upvotes: 2

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