[CentralOH] Handy function to decimate a list of numbers (get every Nth item)

[Mark Erbaugh]

On Wed, 2009-03-18 at 16:48 -0400, Bryan Harris wrote:
> Hey all, I came up with this little snippet to get every Nth line in a list.    
> Google didn't turn anything up in the first few pages.  Does anybody know a 
> better way?  This seems like the kind of thing python would be able to do 
> automatically using the % (modulo) symbol or something.
> 
> Code:
> def decimate(array,points):
>     if type(points) != type(1):  #line 1.5 doesn't mean anything!
>         raise Error, "number of points should be an integer"
>     
>     if len(array)/2<=points:  #Not worth doing for an array this small
>         return array
> 
>     new_array=[]
>     #get the line numbers rather than stepping through the entire list
>     interval=int(len(array)/points)  
>     line_numbers = range(0,len(array),interval)
>     
>     for each in line_numbers:
>         new_array=new_array + [array[each]]
>     return(new_array)
> 
> 


How about array[::points]?

demo:

array = ['Line %d] % i for i in range(100)]

array[::10]

['Line 0', 'Line 10', ... 'Line 90']

Mark