       Re: Need a nice way to do this

• To: mathgroup at smc.vnet.net
• Subject: [mg40313] Re: Need a nice way to do this
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Mon, 31 Mar 2003 04:01:23 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <b63r1a\$3oc\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

UnequalLeft[lst_, symbs_] := Module[{l, i},
Map[
(i = 0;
l[#1] = Map[Function[{x}, If[x =!= #1, i++, i]] , lst]) &,
symbs];

MapIndexed[l[#][[First[#2]]] &, lst]
]

and call it with

UnequalLeft[s, {a, b}]

Regards
Jens

Steve Gray wrote:
>
>         Given a list consisting of only two distinct values, such as
> s={a,b,b,a,a,a,b,a,b,a,a}, I want to derive a list of equal length
> g={0,1,1,2,2,2,4,3,5,4,4}. The rule is: for each position
> 1<=p<=Length[s], look at list s and set g[[p]] to the number of
> elements in s to the left of p which are not equal to s[[p]].
>         In a more general version, which I do  not need now, s would
> not be restricted to only two distinct values.
>
>         Thank you for any ideas, including other applications where
> this particular calculation is used. The current application is an
> unusual conjecture in geometry.

```

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