Re: Partitioning lists
- To: mathgroup at smc.vnet.net
- Subject: [mg20509] Re: Partitioning lists
- From: Hans Staugaard <hans.staugaard at get2net.dk>
- Date: Wed, 27 Oct 1999 02:05:05 -0400
- Organization: get2net Internet Kunde
- References: <7v3dfq$63d@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
DIAMOND Mark wrote:
>
> I would like a function f to split a list as follows
>
> a={1,2,3,4,5,6}
> f[a] =
> {
> {{1},{2,3,4,5,6}},
> {{1,2},{3,4,5,6}},
> {{1,2,3},{4,5,6}},
> {{1,2,3,4},{5,6}},
> {{1,2,3,4,5},{6}}
> }
>
> I can do this as
>
> Table[{Take[a, i], Drop[a, i]}, {i, 1, Length[a] - 1}]
>
> but it *looks* as though it is very inefficient. Is it?
> It also looks as though there should be a way of using Partition simply to
> chop a list between positions i and i+1, but
> I cannot see how to do it. Any suggestions?
>
> mark diamond
> no spam email: markd at psy dot uwa dot edu dot au
Here's a suggestion
In[1]:=
t = Range[6]
Out[1]=
{1, 2, 3, 4, 5, 6}
In[2]:=
ReplaceList[t, {a__, b__} -> {{a}, {b}}]
Out[2]=
{{{1}, {2, 3, 4, 5, 6}}, {{1, 2}, {3, 4, 5, 6}}, {{1, 2, 3}, {4, 5,
6}},
{{1, 2, 3, 4}, {5, 6}}, {{1, 2, 3, 4, 5}, {6}}}
I imagine it is not very efficient for large list.
Hans