Using functional tools

[Chris Emery]

This is how I might do it.

>>> list2 = [list[a] for a in range(len(list)) if not a % 2]
>>> list2
['a', 'c', 'e']

where list[a], you could replace with list[function(a)], and the
if not a % <num>, is how often you want to do it.

for the reading in of files, I belive you really don't have a choice...,
but to write, you can shorten it a bit as such

open("myfile.txt", "w").writelines([list[a] for a in range(len(list)) if
not a % 2])

or something to that affect


My $00.2
Chris

On Sat, 2002-05-04 at 01:37, Pekka Niiranen wrote:
> I would like to feed every second (or 3rd or 4th .etc) item in a list to
> a function.
> 
> list = ['a', 'b', 'c', 'd', 'e']
> 
> **some fancy map/filter -trick here**
> 
> => list = ['a', function('b'), 'c', function('d'), 'e']
> 
> Is there a (functional) way without using for or while -structures ?
> 
> If I only manipulate every second line of a file with that function,
> is there a faster way than reading the whole file into a list ?:
> 
> list = open ("myfile.txt", "rb").readlines()
> **modify every 2nd line with set of functions**
> ** write the whole list into a new file**
> 
> The size of a file is max 2Mb.
> 
> -pekka-
> 
> 
> 
> 
> 
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