How do I alphabetically sort every -n line in a text file, and have the remaining information follow along?

Question

I am trying to sort a text file in alphabetical order (names) but I still want the information regarding the specific persons to follow with the reordering. I know it sounds weird, but an example might help.

Every person has two names, a phone number, en email address, and an address. When I sort the file, I want the information about every specific person to follow with them.

Text file:

Bob Steven
02847661723
[email protected]
Bob Street 121
Alex Ericsson
1233213211
[email protected]
Alex Street 112
Chris Philips
018207129387
[email protected]
Christ Street 902

When sorted, it should be something like this:

Alex Ericsson
1233213211
[email protected]
Alex Street 112
Bob Steven
02847661723
[email protected]
Bob Street 121
Chris Philips
018207129387
[email protected]
Christ Street 902

I found this string of code which kind of works, but it sorts every single line. How do I make it so it only sorts every 4th line (1st line, 5th line and so on)?

input_filename = "filename.txt"
output_filename = "filename.txt"

with open(input_filename, "r") as f:
    l = [line for line in f if line.strip()]

l.sort(key=lambda line: line.split())

with open(output_filename, "w") as f:
    for line in l:
        f.write(line)

Asked By: Voltz

||

Source

Answer 1

You can try:

with open("input.txt", "r") as f_in:
    data = [line for line in map(str.strip, f_in) if line]

data = sorted(
    [data[i : i + 4] for i in range(0, len(data), 4)], key=lambda k: k[0]
)

with open("output.txt", "w") as f_out:
    for chunk in data:
        print(*chunk, file=f_out, sep="n")

This creates output.txt with contents:

Alex Ericsson
1233213211
[email protected]
Alex Street 112
Bob Steven
02847661723
[email protected]
Bob Street 121
Chris Philips
018207129387
[email protected]
Christ Street 902

Answered By: Andrej Kesely

Answer 2

s = """Bob Steven
02847661723
[email protected]
Bob Street 121
Alex Ericsson
1233213211
[email protected]
Alex Street 112
Chris Philips
018207129387
[email protected]
Christ Street 90"""


data = 'n'.join(['n'.join(x) for x in sorted([s.split('n')[i:i+4] for i in range(0, len(s.split('n')), 4)], key=lambda x: x[0])])
print(data)

output:

Alex Ericsson
1233213211
[email protected]
Alex Street 112
Bob Steven
02847661723
[email protected]
Bob Street 121
Chris Philips
018207129387
[email protected]
Christ Street 90

Answered By: 555Russich

Answer 3

Basically, what want to do here is read your file in chunks, and then sort each chunk. Andrej has already demonstrated how to do that, but let’s take it up a notch. Let’s define a class to encapsulate the data for each person. The class contains attributes name, phone, email, address to store each of our data fields, and methods __str__ to convert the class back to a string (to print to screen/file), and __eq__ and __gt__ to define comparison to other objects of the class (to sort). We can also define a class method from_iter that will take in a file handle (or other iterator) and consume its first four elements to define a Person object:

def Person:
    def __init__(self, name, phone, email, address):
        self.name = name
        self.phone = phone
        self.email = email
        self.address = address

    @classmethod
    def from_iter(cls, src):
        return Person(next(src), next(src), next(src), next(src))

    def _as_tuple(self):
        return (self.name, self.phone, self.email, self.address)

    def __repr__(self):
        return f"Person({repr(self.name)}, {repr(self.phone)}, {repr(self.email)}, {repr(self.address)})"

    def __str__(self):
        return "n".join(self._as_tuple())

    def __eq__(self, other):
        return self._as_tuple() == other._as_tuple()

    def __gt__(self, other):
        return self._as_tuple() > other._as_tuple()

Now, we can open the file and pass the handler to the reader function:

people = []
with open(input_filename) as f_in:
    try:
        people.append(Person.from_iter(f_in))
    except StopIteration: # Thrown when the file is exhausted
        pass

Now, we have the following people list:

[Person('Bob Steven', '02847661723', '[email protected]', 'Bob Street 121'),
 Person('Alex Ericsson', '1233213211', '[email protected]', 'Alex Street 112'),
 Person('Chris Philips', '018207129387', '[email protected]', 'Christ Street 902')]

Sorting this list is easy — use the sorted function, and since we already defined the __eq__ and __gt__ methods, the class can figure out how its objects compare to each other. In this case, the _as_tuple() of each object is compared, which simply compares the names first, then the phones, then the emails, and finally the addresses of the two objects. Simply doing sorted(people) gives

[Person('Alex Ericsson', '1233213211', '[email protected]', 'Alex Street 112'),
 Person('Bob Steven', '02847661723', '[email protected]', 'Bob Street 121'),
 Person('Chris Philips', '018207129387', '[email protected]', 'Christ Street 902')]

And to write it back to a file:

sorted_people = sorted(people)

with open(output_filename, "w") as f_out:
    for p in sorted_people:
        f_out.write(str(p)) # Use the __str__ defined in the class
        f_out.write("n") # Because a newline needs to be explicitly written

we get the desired output:

Alex Ericsson
1233213211
[email protected]
Alex Street 112
Bob Steven
02847661723
[email protected]
Bob Street 121
Chris Philips
018207129387
[email protected]
Christ Street 902

Answered By: Pranav Hosangadi

How do I alphabetically sort every -n line in a text file, and have the remaining information follow along?

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