按时间戳使用python对文本文件行进行排序

Question

I have a txt file where line 1-5 are all words and line 6 and above has timestamp at the beginning as shown:

This is a document1
This is a document2
This is a document3
This is a document4
This is a document5
2019-05-27 07:00:00, value1, value2, value3
2019-05-27 06:38:00, value1, value2, value3
2019-05-27 07:05:00, value1, value2, value3

How can I sort lines 6 to the last line where the earliest time is on top and latest time at below?

This is what I have attempted based on another stack overflow question but did not work.

  lines = sorted(open(outputFile.txt).readlines(), key=lambda line: line[5:-1].split(",")[0])
  outFile.close()

Answer 1

If you don't "need" a one-liner, you can do the following:

# Read all lines
with open("file.txt") as f:
    lines = f.readlines()

# Keep only from 6th line
lines = lines[5:]
# Sort based on the date of each line
lines.sort(key = lambda l : l.split(',')[0])

Untested, but should work.

Answer 2

You can read the file as a pandas DataFrame and then use sort_values() on the according lines.

Also, I'd recommend to cast the columns to their type and transfer the table into a tidy format -> here the first column should only be of datetime

With this approach you'd basically have two lines (w/o casting):

df = read_csv('name_of_file.txt', sep='\t', skiprows=5, header=None, names=['first_col'])
df.sort_values('first_col', ascending=True)

Answer 3

Here (in1.txt is the data from the post)

from datetime import datetime

with open('in1.txt') as f:
    sorted_lines = sorted([l.strip() for l in f.readlines()][5:],
                          key=lambda line: datetime.strptime(line.split(",")[0], "%Y-%m-%d %H:%M:%S"))
    for line in sorted_lines:
        print(line)

output

2019-05-27 06:38:00, value1, value2, value3
2019-05-27 07:00:00, value1, value2, value3
2019-05-27 07:05:00, value1, value2, value3