Sort a list of strings based on regular expression match

Question

I have a text file that looks a bit like:

random text random text, can be anything blabla %A blabla
random text random text, can be anything blabla %D blabla         


        

Answer 1

You could use a custom key function to compare the strings. Using the lambda syntax you can write that inline, like so:

strings.sort(key=lambda str: re.sub(".*%", "", str));

The re.sub(".*%", "", str) call effectively removes anything before the first percent sign so if the string has a percent sign it'll compare what comes after it, otherwise it'll compare the entire string.

Pedantically speaking, this doesn't just use the letter following the percent sign, it also uses everything after. If you want to use the letter and only the letter try this slightly longer line:

strings.sort(key=lambda str: re.sub(".*%(.).*", "\\1", str));

Answer 2

what about this? hope this helps.

def k(line):
    v = line.partition("%")[2]
    v = v[0] if v else 'z' # here z stands for the max value
    return v
print ''.join(sorted(open('data.txt', 'rb'), key = k))

Answer 3

Here is a quick-and-dirty approach. Without knowing more about the requirements of your sort, I can't know if this satisfies your need.

Assume that your list is held in 'listoflines':

listoflines.sort( key=lambda x: x[x.find('%'):] )

Note that this will sort all lines without a '%' character by their final character.

Answer 4

In [1]: def grp(pat, txt): 
   ...:     r = re.search(pat, txt)
   ...:     return r.group(0) if r else '&'

In [2]: y
Out[2]: 
['random text random text, can be anything blabla %A blabla',
 'random text random text, can be anything blabla %D blabla',
 'random text random text, can be anything blabla blabla %F',
 'random text random text, can be anything blabla blabla',
 'random text random text, %C can be anything blabla blabla']

In [3]: y.sort(key=lambda l: grp("%\w", l))

In [4]: y
Out[4]: 
['random text random text, can be anything blabla %A blabla',
 'random text random text, %C can be anything blabla blabla',
 'random text random text, can be anything blabla %D blabla',
 'random text random text, can be anything blabla blabla %F',
 'random text random text, can be anything blabla blabla']