Pattern Matching Given # of Characters and no String Input; use RegularExpressions?

[tiissa]

Synonymous wrote:
> tiissa <tiissa at nonfree.fr> wrote in message news:<42623ba8$0$10322$636a15ce at news.free.fr>...
> 
>>tiissa wrote:
>>
>>>If you know the number of characters to match can't you just compare 
>>>slices?
>>
>>If you don't, you can still do it by hand:
>>
>>In [7]: def cmp(s1,s2):
>>   ....:     diff_map=[chr(s1[i]!=s2[i]) for i in range(min(len(s1), 
>>len(s2)))]
>>   ....:     diff_index=''.join(diff_map).find(chr(True))
>>   ....:     if -1==diff_index:
>>   ....:         return min(len(s1), len(s2))
>>   ....:     else:
>>   ....:         return diff_index
>>   ....:
> 
> I will look at that, although if i have 300 images i dont want to type
> all the comparisons (In [9]: cmp('ccc','cccap')) by hand, it would
> just be easier to sort them then :).

I didn't meant you had to type it by hand. I thought about writing a 
small script (as opposed to using some in the standard tools). It might 
look like:

In [22]: def make_group(L):
    ....:     root,res='',[]
    ....:     for i in range(1,len(L)):
    ....:         if ''==root:
    ....:             root=L[i][:cmp(L[i-1],L[i])]
    ....:             if ''==root:
    ....:                 res.append((L[i-1],[L[i-1]]))
    ....:             else:
    ....:                 res.append((root,[L[i-1],L[i]]))
    ....:         elif len(root)==cmp(root,L[i]):
    ....:             res[-1][1].append(L[i])
    ....:         else:
    ....:             root=''
    ....:     if ''==root:
    ....:         res.append((L[-1],[L[-1]]))
    ....:     return res
    ....:

In [23]: L=['cccat','cccap','cccan','dddfa','dddfg','dddfz']

In [24]: L.sort()

In [25]: make_group(L)
Out[25]: [('ccca', ['cccan', 'cccap', 'cccat']), ('dddf', ['dddfa', 
'dddfg', 'dddfz'])]


However I guarantee no optimality in the number of classes (but, hey, 
that's when you don't specify the size of the prefix).
(Actually, I guarantee nothing at all ;p)
But in particular, you can have some file singled out:

In [26]: make_group(['cccan','cccap','cccat','cccb'])
Out[26]: [('ccca', ['cccan', 'cccap', 'cccat']), ('cccb', ['cccb'])]


It is a matter of choice: either you want to specify by hand the size of 
the prefix and you'd rather look at itertools as pointed out by Kent, or 
you don't and a variation with the above code might do the job.