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}}}