Regex function to extract selected rows

Question

I have a text file like this

Some text and random stuff that I don't need

2 8 
2 9 T
4 9
1 10 
2 10 F
7 11 T

More random stuff

How should I construct a regex function to extract both the rows with just numbers and the rows with numbers and T or F?
So far my idea for the code is this

with open(file, 'r') as log_file:
    # opening file
        file = log_file
        while True:
            line = file.readlines()
            
            # if line in regex function:

                data.append(line)
                # closing file
                break

How can I solve this?

Asked By: Lorenz

||

Source

Answer 1

With this approach, the re pattern will match only numbers or numbers that end with the letter T or F. You could also use a for loop instead of a while loop.

import re

matched_data = []
with open(file, 'r') as log_file:
    data = log_file.readlines()
    
    for line in data:
        line = line.strip()
        if re.match(r'^d+ d+( [TF])?$', line):
            matched_data.append(line)
    
print(matched_data)

if some of the lines starts with a letter eg; T 7 11 and you want to match those as well, you should substitute the above pattern with r'^[TF]|d+ d+( [TF])?$'
Test Code:

import re

data = """
2 8 
2 9 T
4 9
1 10 
2 10 F
7 11 T
5 B 37
Y 9 G
T 7 11
MG 99 Z
"""

data = data.splitlines()
matched_data = []
for line in data:
    line = line.strip()
    if re.match(r'^d+ d+( [TF])?$', line):
        matched_data.append(line)
        
print(matched_data)
# ['2 8', '2 9 T', '4 9', '1 10', '2 10 F', '7 11 T']

Answered By: Jamiu S.

Answer 2

We can use re.findall() to get all the occurences, in the entire file.

import re

regexp = r"^d[d ]*[T|F]?"

with open("file.txt", "r") as fp:
    # Not suggested if the file is large.
    data = fp.read()
    print(re.findall(regexp, data, re.M))

output:

['2 8 ', '2 9 T', '4 9', '1 10 ', '2 10 F', '7 11 T']

For large file, Its better to iterate line by line.

data = []
regexp = r"^d[d ]*[T|F]?"
with open(file, 'r') as fp:
    for line in fp:
        _match = re.match(regexp, line)
        if _match:
            data.append(_match.group())

If you are interested in learning more about regular expressions, visit regexone

Answered By: mutyalu

Answer 3

You might as well parse the lines you match to tuples of (int, int, boolean |None):

import re

with open("file.txt", "r") as file:
    result = [
        (int(a), int(b), flag == "T" if flag else None)
        for a, b, flag in re.findall(r"^(d+)[ ]+(d+)(?:[ ]+([TF]))?[ ]*$", 
                                     file.read(), re.M)
    ]

print(result)

Output for the example file:

[(2, 8, None), (2, 9, True), (4, 9, None), (1, 10, None), (2, 10, False), (7, 11, True)]

Answered By: trincot

Regex function to extract selected rows

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