Python unusual file sorting

Question

I have a txt file that contains data in the following fashion:

23       1      65      15      19.2
19       2      66      25      25.7
10       3      67      35      16.5
100      4      68      45      10.4
20       5      69      55      6.8
201      6      64      65      9.2

Within the file, each value is separated from other using \t and then \n for next line.

I want to sort this file based on the first values of the each line. My expected output is :

10       3      67      35      16.5
19       2      66      25      25.7
20       5      69      55      6.8
23       1      65      15      19.2
100      4      68      45      10.4
201      6      64      65      9.2

But the actual output I am getting is as:

10       3      67      35      16.5
100      4      68      45      10.4
19       2      66      25      25.7
20       5      69      55      6.8
201      6      64      65      9.2
23       1      65      15      19.2

Its taking the values as strings and hence not taking the entire numbers value as integer. I tried parsing, but its not working.

My code:

with open('filename.txt') as fin:
        lines = [line.split() for line in fin]
lines.sort(key=itemgetter(0),reverse=True)

with open('newfile.txt', 'w') as fout:
    for i in lines:
            fout.write('{0}\t\t\t\t\n'.format('\t\t\t '.join(i)))

Please help if possible.

Answer 1

You're currently comparing strings, you need to compare integers:

lines.sort(key=lambda x:int(x[0]), reverse=True)

Strings are compared lexicographically, so:

>>> '2' > '100'
True

Conversion to int fixes this issue:

>>> int('2') > int('100')
False

Answer 2

Also take a look at pandas, if you plane to make more complicated manipulations later, for example:

import pandas as pd

pd.read_table('filename.txt', header=None)\
            .sort(columns=0)\
            .to_csv('newfile.txt', sep='\t', header=None, index=False)