How to sort an output file based on second parameter?

Question

I am trying to sort a result I write into an output file after a certain character ':' by the integer after the character.

First, I tried using sort function but it did not work as it was not a list. I also tried to convert everything to string list and tried to sort accordingly but do not think it’s the most efficient way to go.

NOTE: output file lines are all strings

**Current written output in output_file1.txt:**
hi: 011
hello: 000
hero: 001
You are done!

**Expected written output in output_file1.txt:**
hello: 000
hero: 001
hi: 011
You are done!

Thank you for your help.

You can't sort the file in place with python. You will need to put the entire file into memory to sort it or you can sort it using a unix shell. Sorting a text file alphabetically (Python) — Error - Syntactical Remorse
– Error - Syntactical Remorse, Commented Apr 16, 2019 at 13:40

Preetham · Accepted Answer · 2019-04-16 16:42:46Z

1

with open(filepath) as file:
    r = file.readlines()

#splits based on ":" and then sort using the second value ie binary numbers
s = sorted([line.split(":") for line in r[1:-1]], key=lambda x: int(x[1]))

s.insert(0,r[0])
s.append(r[-1])

#Write 's' into File

answered Apr 16, 2019 at 16:42

Preetham

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jDoe · Accepted Answer · 2019-04-16 13:44:51Z

I would the insert the lines in order from the very beginning, you can do that efficiently using binary search.

Q: How to compare the current number in the current line with your old file.

Answer:

Case 1: If the maximum number of lines is 111, (in your example you start with 001, I assume you padded with zeros to show how many digits you expect per number) or you now the max number of lines, you can pad with a sufficient number of zeros, then all you have to do is compare you current number with the current last three entries in your line (line[-3:]).

Case 2: You don't know the number of digits:

Sol 2.1: You can try storing a file for words and a file for numbers, and update them in parallel, this will save you from the overhead of Sol 2.2.

Sol 2.2: Split the line by delimiter ':' and get the number (don't forget that you have a space after the delimiter).

That is what I could come up with for now!

fluxens · Accepted Answer · 2019-04-16 13:47:48Z

0

As mentioned above, there is no way to sort a file in place.

Regarding your second question, you can use list.sort(key=sort_key). This allows you to supply a method which is applied to every element in your list when comparing the elements for sorting.

In your case you can define a simple function which extracts the last three characters and sort them alphabetically:

def num_sort(x):
   return x[-3:]
your_list.sort(key=num_sort)

answered Apr 16, 2019 at 13:47

fluxens

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