Difference between 2 files in order

Question

I am trying to copy string line from file2 to file1, if this line is not exist in file1. I am using symmetric_difference but it gives me unordered result. Content of files in this example is not actual. There is no numbers in my actual files, just strings, but I used numbers to show the problem. I could probably add numbers to file 2 and sort it as list, but file 2 randomly getting information from other program, that I am not familiar with, and don't want to interfere.

content of file1:

'1\n','2\n','3\n'

content of file2:

'1\n','2\n','3\n','4\n'`,'5\n','6\n','7\n','8\n','9\n','10\n'

it's just string on every line

diff = set(file1).symmetric_difference(file2)

set(['8\n', '10\n', '9\n', '6\n', '7\n', '4\n', '5\n'])

My goal is

set(['4\n', '5\n', '6\n', '7\n', '8\n', '9\n', '10\n'])

a `set` has no defined order. – juanpa.arrivillaga Mar 10 '17 at 00:33 — juanpa.arrivillaga, Mar 10 '17 at 00:33

score 1 · Answer 1 · answered Mar 10 '17 at 00:16

1

use join() and split()

line1 = "'1\n','2\n','3\n'"
line2 = "'1\n','2\n','3\n','4\n'`,'5\n','6\n','7\n','8\n','9\n','10\n'"

''.join([i for i in line2.split(',') if i not in line1.split(',')])

answered Mar 10 '17 at 00:16

plasmon360

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score 1 · Answer 2 · answered Mar 10 '17 at 00:17

1

You can do this from the set obtained by symmetic_difference:

a_list = list(set_instance)
a_list.sort()

then you have a sorted list and you can append to the file1

answered Mar 10 '17 at 00:17

Mikedev

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score 1 · Answer 3 · edited May 23 '17 at 12:09

1

If you aren't married to python, this can be done very easily with the comm Unix executable (if you're on a Unix based system):

$ comm -13 file1.txt file2.txt
4
5
6
7
8
9
10

This assumes the files are pre-sorted.

You could easily call this from Python.

More info on how to use comm

edited May 23 '17 at 12:09

Community

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answered Mar 10 '17 at 00:32

Julien

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score 0 · Answer 4 · answered Mar 10 '17 at 00:09

0

For now I am using

with open("file2") as f:
    with open("file1", "r+") as f1:
        for line in f:
            if line not in f1:
                f1.write(line)

answered Mar 10 '17 at 00:09

Pavel Vanchugov

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score 0 · Answer 5 · answered Mar 10 '17 at 00:19

If you transform a list into a set, the order of the elements will be lost. That's totally normal because mathematically the order is meaningless into a set. You will have to reorder it afterwards if you are using set.symmetric_difference. If this wont give you the a satisfactory result, than you should write your own algorithm.

Difference between 2 files in order

5 Answers5