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Topic: split the sublists into parts according to some rules
Replies: 2   Last Post: Sep 4, 2012 5:46 AM

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Ray Koopman

Posts: 3,382
Registered: 12/7/04
Re: split the sublists into parts according to some rules
Posted: Sep 4, 2012 5:46 AM
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On Sep 3, 12:01 am, Ray Koopman <koop...@sfu.ca> wrote:
> On Aug 31, 1:01 am, Joug Raw <joug...@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}}}


Here are two alternate versions of the sublist splitter:

subsplitr2[sublist_,r_] := With[{n = Length@sublist}, If[n < r, {},
Take[sublist,#]& /@ Transpose@{Most@#+1,Rest@#}& @
FoldList[Plus,0,Floor[n/r] + UnitStep[Mod[n,r]-Range@r]]]]

subsplitr3[sublist_,r_] := With[{n = Length@sublist}, If[n < r, {},
Take[sublist,#]& /@ Transpose@{Prepend[Most@#+1,1],#}&[
Floor[n/r]*Range@r + Clip[Range@r,{1,Mod[n,r]}]]]]




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