Pattern finding LZW python

Question

LZW algorithm is used to find patterns between input symbols. But can it seek pattern among words ? I mean the alfabet index not to be symbols but words for example for the input :

'abcd', 'abcd', 'fasf' , 'asda', 'abcd' , 'fasf' ...

to have an output like :

'abcd', '1', 'fasf' , 'asda' , '1', '2' ...

Or is there any compressing algorithm that does the trick ?

Joran Beasley · Accepted Answer · 2014-03-12T21:51:52.723

1

keys = []
def lzw(text):
      tokens = text.split()
      new_keys = dict.fromkeys(tokens).keys()
      keys.extend([key for key in new_keys if  key not in keys])
      encoded = ["%s"%keys.index(tok) for tok in tokens]
      for i,key in enumerate(keys):
           try:
              encoded[encoded.index(str(i))] = key
           except:
               pass
      return " ".join(encoded)

print lzw("abcd abcd fasf asda abcd fasf")
#outputs: abcd 0 fasf asda 0 2

is a pretty easy implementation

edited Mar 12 '14 at 21:51

answered Mar 12 '14 at 21:23

Joran Beasley

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this actually doesnt do what you want I think I misunderstood the problem you were having sorry :( ... – Joran Beasley Mar 12 '14 at 21:31
I want to use this for many deifferent lists but I do want to keep the same index keys. So for every list I input the text and output the compressed text and the keys () to pass the to the next list for compression right ? – bill Mar 12 '14 at 21:45
there now it should preserve your keys – Joran Beasley Mar 12 '14 at 21:52
and the decompress i guess will be with something like re.match(keys, word), right? – bill Mar 12 '14 at 21:57
1

or something like `re.sub("\s\d+\s",lambda g:keys[int(g.groups()[0])])` – Joran Beasley Mar 12 '14 at 22:02

score 0 · Answer 2 · answered Mar 12 '14 at 21:25

You can use this code which will search through strings to find a pattern. You will need to know what pattern you want to search for though.

## Search for pattern 'iii' in string 'piiig'.
## All of the pattern must match, but it may appear anywhere.
## On success, match.group() is matched text.
match = re.search(r'iii', 'piiig') =>  found, match.group() == "iii"
match = re.search(r'igs', 'piiig') =>  not found, match == None

Have a read of this website: https://developers.google.com/edu/python/regular-expressions?hl=iw

Pattern finding LZW python

2 Answers2