Compress a string

[Gary Herron]

Matt Porter wrote:
> Hi guys,
>
> I'm trying to compress a string.
> E.g:
>  "AAAABBBC" -> "ABC"
>
> The code I have so far feels like it could be made clearer and more 
> succinct, but a solution is currently escaping me.
>
>
> def compress_str(str):
>     new_str = ""
>     for i, c in enumerate(str):
>         try:
>             if c != str[i+1]:
>                 new_str += c
>         except IndexError:
>             new_str += c
>     return new_str
>
>
> Cheers
> Matt

This is shorter and perhaps clearer:

def compress_str(str):
   new_str = ""
   for c in str:
     if not new_str  or  c != new_str[-1]:
       new_str += c
   return new_str


However, successive appends to a string is inefficient (whereas 
successive appends to a list are ok), so this is probably more efficient:

def compress_str(str):
   r = []
   for c in str:
     if not r  or  c != r[-1]:
       r.append(c) # Build a list of characters
   return ''.join(r)#  Join list into a single string


And then building a list in a loop is usually more efficient (and 
perhaps clearer) if done with a list comprehension:

  new_str = ''.join([c for i,c in enumerate(str)   if not i or str[i-1] 
!= c])

or, maybe clearer as two lines:

  r = [c for i,c in enumerate(str)   if not i or str[i-1] != c]
  new_str = ''.join(r)


Gary Herron