Re: 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(st r):
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(st r):
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(st r):
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

[Paul McGuire]

Re: Compress a string

On May 18, 1:45 pm, Gary Herron <gher...@island training.comwro te:

Matt Porter wrote:

Hi guys,

>

I'm trying to compress a string.
E.g:
 "AAAABBBC" -"ABC"

>

I'm partial to using (i)zip when I need to look at two successive
elements of a sequence:

>>from itertools import izip
>>instr = "aaaaaaaaaaabbb bbbbbbbdddddaaa aaaaddddddccccc cc"
>>newstr = "".join( b for a,b in izip(" "+instr,ins tr) if a!=b )
>>print newstr

abdadc

-- Paul