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Re: split the sublists into parts according to some rules

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  • Subject: [mg127933] Re: split the sublists into parts according to some rules
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Mon, 3 Sep 2012 02:55:29 -0400 (EDT)
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On Aug 31, 1:01 am, Joug Raw <joug... at gmail.com> wrote:
> Dear all,
>
> I have a long list which has many sublists inside,
>
> Thelonglist={{a,b,c,d,e},{x,y,z},{a1,a2,a3,a4},...}
>
> Each sublist has length > 1(no single element sublist exists) . And the
> lengths of the sublists are different and unknow in advanced. The length of
> some of the sublists are odd number, such as {a,b,c,d,e} and {x,y,z}. Some
> sublists have even number list length, like {a1,a2,a3,a4}.
>
> What I want to achieved is to split each sublist into two (or three, or
> more) parts. In the two parts case, if the length of original sublist is
> even number, the two new parts will have same length, e.g, {a1,a2,a3,a4}
> become {{a1,a2},{a3,a4}}. If the sublist has length in odd number,
> after splitting one of the two parts should have one more element than the
> other.
>
> That is,
> Input: Thelonglist={{a,b,c,d,e},  {x,y,z},  {a1,a2,a3,a4},...}
> Output: Newlist={{a,b,c}, {d,e}},  {{x,y}, {z}},  {{a1,a2}, {a3,a4}},...}
>
> Or the same idea for the three parts case,
> Input: Thelonglist={{a,b,c,d,e},  {x,y,z},  {a1,a2,a3,a4},...}
> Output: Newlist={{{a,b}, {c,d}, {e}},  {{x},{y},{z}},  {{a1}, {a2},
> {a3,a4}}, ...}
>
> For the case of 4 parts, the number 4 is larger than the length of some
> sublists and I will abandon those list with short length.
> Input: Thelonglist={{a,b,c,d,e},  {x,y,z},  {a1,a2,a3,a4},...}
> Output: Newlist={{{a}, {b}, {c}, {d,e}},  {{a1}, {a2}, {a3}, {a4}}, ...}
>
> Could there be a simple function to achieve this idea generally? Say, a
> function like *SplittoPart[**list_*, *partnumber_**]*, in which I just need
> to give the input list and the number of parts of sublists I want to have.
> Then it will do the job above. If the number of sublist is larger then the
> length of some sublists, the function just abandon those short list and do
> the split(or partition) work on the other lists with long enough length.
> Could some one help me on this?
>
> If that is too complicated, I would still be happy to see some one could
> give me a solution only for the case of splitting to two parts,
>
> Input: Thelonglist={{a,b,c,d,e},  {x,y,z},  {a1,a2,a3,a4},...}
> Output: Newlist={{a,b,c}, {d,e}},  {{x,y}, {z}},  {{a1,a2}, {a3,a4}},...}
>
> Thanks a lot for your kind help!

splitr[list_,r_] := subsplitr[#,r]&/@list/.{}->Sequence[]

subsplitr[sublist_,r_] := With[{n = Length@sublist}, If[n < r, {},
Take[sublist,#]& /@ (Transpose@{Most@#+1,Rest@#}&)[
FoldList[Plus,0,Floor[n/r]+Boole@Thread[Range@r<=Mod[n,r]]]]]]

longlist = {{a, b, c, d, e}, {x, y, z}, {a1, a2, a3, a4}};

splitr[longlist,2]

{{{a, b, c}, {d, e}}, {{x, y}, {z}}, {{a1, a2}, {a3, a4}}}

splitr[longlist,3]

{{{a, b}, {c, d}, {e}}, {{x}, {y}, {z}}, {{a1, a2}, {a3}, {a4}}}

splitr[longlist,4]

{{{a, b}, {c}, {d}, {e}}, {{a1}, {a2}, {a3}, {a4}}}



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