CODEWITHSUNDEEP
pythonpython-3.xlist
Murray
Murray

Reputation: 57

python - merging lists from 2 text files

I'm very new to Python. I want to take the contents of 2 text files, convert them into 2 lists, merge them together and order them from smallest to biggest.

Converting them to lists seems easy, but I can't merge properly for the ordering.

They come out like this (a list of lists instead of a single list): ['[0, 4, 6, 6, 22, 23, 44]', '[1, 4, 5, 6, 7, 22, 777]']

Here's my code:

with open('numbers1.txt','r') as newfile1:
    list1 = newfile1.read().splitlines()
    print (list1)

with open('numbers2.txt','r') as newfile2:
    list2 = newfile2.read().splitlines()
    print (list2)

merged = []
for i in range(0, len(list1)) :
    merged.append(list1[i])
    merged.append(list2[i])
print(merged)

Thanks in advance for any assistance.

Upvotes: 2

Views: 1024

Answers (1)

Raoslaw Szamszur
Raoslaw Szamszur

Reputation: 1740

First of all, to join to lists you can use simple + operator:

>>> l1 = [1, 2, 3]
>>> l2 = [4, 5, 6]
>>> merged = l1 + l2
>>> print(merged)
[1, 2, 3, 4, 5, 6]

Now for sorting use python built-in sort() function:

Python lists have a built-in list.sort() method that modifies the list in-place. By default, sort() doesn't require any extra parameters. However, it has two optional parameters:

reverse - If true, the sorted list is reversed (or sorted in Descending order)

key - function that serves as a key for the sort comparison

>>> l1 = [1, 2, 3]
>>> l2 = [4, 5, 6]
>>> merged = l2 + l1
>>> print(merged)
[4, 5, 6, 1, 2, 3]
>>> merged.sort(key=int)
>>> print(merged)
[1, 2, 3, 4, 5, 6]

Edit

@Murray above-mentioned solution works just fine but it doesn't fit your use case since in your text files you have list alike string:

This is numbers1.txt: [0, 4, 6, 6, 22, 23, 44] and this is numbers2.txt: [1, 4, 5, 6, 7, 22, 777] – Murray 1 hour ago

Now when you read file as list1/list2 actually you'll get a list with one element which is a string.

>>> with open("numbers1.txt", "r") as f:
...     print(list1)
...     print(type(list1))
...     print(len(list1))
...     print(type(list1[0]))
... 
['[0, 4, 6, 6, 22, 23, 44]']
<type 'list'>
1
<type 'str'>

In order to append those numbers from file you'll need to parse them first. It can be achieved like so (depending on your exact use case final solution may vary):

$ cat numbers1.txt 
[0, 4, 6, 6, 22, 23, 44]
$ cat numbers2.txt 
[1, 4, 5, 6, 7, 22, 777]
$ cat test.py 
files = ['numbers1.txt', 'numbers2.txt']
merged = []

for f in files:
    with open(f,'r') as lines:
        for line in lines:
            for num in line.rstrip().strip('[]').split(', '):
                merged.append(int(num))

print(merged)
merged.sort()
print(merged)
$ python test.py 
[0, 4, 6, 6, 22, 23, 44, 1, 4, 5, 6, 7, 22, 777]
[0, 1, 4, 4, 5, 6, 6, 6, 7, 22, 22, 23, 44, 777]
$ python3 test.py 
[0, 4, 6, 6, 22, 23, 44, 1, 4, 5, 6, 7, 22, 777]
[0, 1, 4, 4, 5, 6, 6, 6, 7, 22, 22, 23, 44, 777]

Now let me break down this code into pieces:

  1. First of all open file(s). I have done it with for loop so I don't have to repeat with open... every time I want to open something (It's just easier and the code is more readable).
  2. Read all lines from a file. (I've assumed that your file can have more than just one line with list like string)
  3. Parse each line and append to list.
    • line.rstrip() - remove a trailing newline
    • .strip('[]') - remove square brackets from string
    • .split(', ') - split string by comma and space to get array of string characters
    • merged.append(int(num)) for each character parse it to int and append to list.
  4. Last but not least sort list.

Upvotes: 2

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