Re: Building List

*To*: mathgroup at smc.vnet.net*Subject*: [mg48043] Re: Building List*From*: "Steve Luttrell" <steve_usenet at _removemefirst_luttrell.org.uk>*Date*: Sat, 8 May 2004 01:23:48 -0400 (EDT)*References*: <c7fhhg$o9u$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

This does what you want: L = { {1, 2}, {3, 4, 5, 6}, {7, 8} }; L /. {x_Integer, y1_Integer, y2 : _Integer ..} :> Apply[Sequence, Map[{x, #} &, {y1, y2}]] The pattern {x_Integer,y1_Integer,y2:_Integer..} matches lists of 3 or more integers, and :> Apply[Sequence, Map[{x, #} &, {y1, y2}]] implements the replacement that you defined. Steve Luttrell "Bruce W. Colletti" <bcolletti at compuserve.com> wrote in message news:c7fhhg$o9u$1 at smc.vnet.net... > Re Mathematica 5.0.1.0. > > I have a list of lists -- e.g., L = { {1,2},{3,4,5,6},{7,8} } -- and > want to replace element-lists (whose length exceeds 2) with another list > built from that element. All else is untouched. > > For instance, using L above, replace {3,4,5,6} with {3,4}, {3,5}, {3,6}. > This transforms L to the desired form { {1,2}, {3,4}, {3,5}, {3,6}, > {7,8} }. > > Although I can do this using Sow and Reap, am hoping there's an easier > way using rules (/.). In general, I want to replace those L-elements x > (that meet a criterion) with foo[x]. > > Thanks. > > Bruce >