Re: List Partition

*To*: mathgroup at smc.vnet.net*Subject*: [mg53941] Re: [mg53895] List Partition*From*: John Kiehl <john.kiehl at soundtrackny.com>*Date*: Fri, 4 Feb 2005 04:12:26 -0500 (EST)*Reply-to*: John Kiehl <john.kiehl at soundtrackny.com>*Sender*: owner-wri-mathgroup at wolfram.com

On Wednesday, February 2, 2005 6:25 AM, zak <chocolatez at gmail.com> wrote: >what could i do to partition the list: >a={cat,E,in,the,hat,E,okay,fine,E} >into >a={{cat},{{in},{the},{hat}},{{okay},{fine}}} > >ie: every word in a sublist , and E determine the end of a >sentence >(a bigger list). >zak > > In[16]:= a={cat,E,in,the,hat,E,okay,fine,E} Out[16]= {cat,E,in,the,hat,E,okay,fine,E} This solution is an automation of this basic idea. In[61]:= Part[a,{1}] Out[61]= {cat} In[62]:= Part[a,{3,4,5}] Out[62]= {in,the,hat} In[63]:= Part[a,{7,8}] Out[63]= {okay,fine} The "Position" of E in the original list will be used to calculate the start and end of each sub-list. (*-------------------------------------------------*) (* so, first put brackets around each element as requested *) In[20]= aa=Map[List,a] Out[20]= {{cat},{E},{in},{the},{hat},{E},{okay},{fine},{E}} (* in general, we want to find positions of {E} in list *) In[30]= pos = Position[aa,{E}]//Flatten Out[30]= {2,6,9} (* one less than pos will be end of each sublist *) In[33]:= last=pos-1 Out[33]:= {1,5,8} (* one more than pos will be start of each sublist, also drop last value and prepend a 1 *) In[41]:= first=Drop[Flatten[{1,pos}],-1] Out[41]= {1,3,7} (* pair these up *) In[45]:= t=Transpose[{first,last}] Out[45]= {{1,1},{3,5},{7,8}} (* map Part[...] over our list t *) In[52]:= Part[aa,Range[Sequence @@ #]]& /@ t Out[52]= {{{cat}},{{in},{the},{hat}},{{okay},{fine}}}