RE: Building List
- To: mathgroup at smc.vnet.net
- Subject: [mg48035] RE: [mg48015] Building List
- From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
- Date: Sat, 8 May 2004 01:23:39 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
>-----Original Message----- >From: Bruce W. Colletti [mailto:bcolletti at compuserve.com] To: mathgroup at smc.vnet.net >Sent: Friday, May 07, 2004 10:30 AM >To: mathgroup at smc.vnet.net >Subject: [mg48035] [mg48015] Building List > > >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 > > If all your sublists are of even length, it's easy: In[1]:= l = {{1, 2}, {3, 4, 5, 6}, {7, 8}}; In[2]:= Partition[Flatten[l, 1], 2] Out[2]= {{1, 2}, {3, 4}, {5, 6}, {7, 8}} ...else, if you then drop the last elements: In[3]:= l2 = {{1, 2}, {3, 4, 5, 6, 6.5}, {7, 8}}; In[4]:= Flatten[#, 1] &[Partition[#, 2] & /@ l2] Out[4]= {{1, 2}, {3, 4}, {5, 6}, {7, 8}} ...or if you want to retain it (as singleton): In[5]:= Flatten[#, 1] &[Partition[#, 2, 2, {1, 1}, {}] & /@ l2] Out[5]= {{1, 2}, {3, 4}, {5, 6}, {6.5}, {7, 8}} ...or retain the first element as singleton: In[21]:= Flatten[#, 1] &[ Partition[#, 2, 2, {1 + Mod[Length[#], 2], 1}, {}] & /@ l2] Out[21]= {{1, 2}, {3}, {4, 5}, {6, 6.5}, {7, 8}} ...?? -- Hartmut Wolf