Re: List difference using patterns and substitutions.
- To: mathgroup at smc.vnet.net
- Subject: [mg71361] Re: [mg71306] List difference using patterns and substitutions.
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Wed, 15 Nov 2006 06:45:47 -0500 (EST)
- Reply-to: hanlonr at cox.net
a={1,2,3,5,5};
Rest[a]-Most[a]
{1,1,2,0}
Most is available in version 5 and later.
Rest[a]-Drop[a,-1]
{1,1,2,0}
ListConvolve[{1,-1},a]
{1,1,2,0}
Partition[a,2,1]/.{x_,y_}:>y-x
{1,1,2,0}
Thread[{Rest[a],Most[a]}]/.{x_,y_}:>x-y
{1,1,2,0}
Bob Hanlon
---- Nacho <ncc1701zzz at gmail.com> wrote:
> Hello.
>
> I'm trying to figure how can I build a difference list from another
> using only patterns and rule substitutions.
>
> The idea is to get from a list, another, one element shorter, where
> each value is the substraction of two consecutive elements in the
> original list, that is, from {1,2,3,5,5} get {1,1,2,0}.
>
> I've been thinking about it for a while, and I know several methods
> using a more traditional programming style (with For, for example), but
> I have no idea if it is possible to make it simple and fast with rule
> substitutions.
>
> Any idea?
>
> Thanks in advance.
>