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Re: match 1, replace 2

• To: mathgroup at smc.vnet.net
• Subject: [mg56244] Re: match 1, replace 2
• From: "Carl K. Woll" <carlw at u.washington.edu>
• Date: Wed, 20 Apr 2005 05:30:31 -0400 (EDT)
• Organization: University of Washington
• References: <d42khj$3ac$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

"Trevor Baca" <trevorbaca at gmail.com> wrote in message 
news:d42khj$3ac$1 at smc.vnet.net...
> hi mathgroup,
>
> what rule takes
>
> ls = {{1, 2, 3}, {4, 5}, {6, 7, 8, 9}}
>
> to
>
>      {{101, -1, 102, -1, 3}, {104, -1, 5}, {106, -1, 107, -1, 108, -1,
> 9}}
>
> ie, matches all integers but the last in each list and then replaces
> each matched integer n with the 2-element sequence Sequence[100 + n,
> -1]?
>
> trevor.
>

Here is one possibility.

n=101;
ls /. {a__Integer, b_Integer} :> Append[{a} /. c_Integer:>Sequence[n++,-1], 
n++; b]

{{101, -1, 102, -1, 3}, {104, -1, 5}, {106, -1, 107, -1, 108, -1, 9}}

Carl Woll