Re: There must be a better way!
- To: mathgroup at smc.vnet.net
- Subject: [mg2342] Re: There must be a better way!
- From: zizza at willamette.edu (Frank Zizza)
- Date: Wed, 25 Oct 1995 02:13:25 -0400
- Organization: Willamette University, Salem, OR, USA
In article <DGxuMB.G69 at wri.com> pehowland at taz.dra.hmg.gb () writes:
>
> Hi. I'm trying to write a function that partitions a list into
> segments of length given by another length. eg.
> Given l1 = {A,B,C,D,E,F,G,H,I,J}
> and l2 = {2,3,4,1}
> I want to be able to say
> In[1] := MyPartition[l1, l2]
> and get
> Out[1] = {{A,B}, {C,D,E}, {F,G,H,I}, {J}}
>
> I've racked my brains, but have been unable to think of an elegant
> solution, but instead managed the following Fortran-like function:
>
> MyPartition[list1_, list2_] :=
> Module[{ans,l},
> ans={};
> l = list1;
> Do [
> AppendTo[ans, Take[l, list2[[i]]]];
> l = Drop[l, list2[[i]]],
> {i, Length[list2]}
> ];
> ans
> ]
>
> Someone put me out of my misery! How can I code this in a more
efficient
> manner?!
>
> Paul E Howland Tel. +44 (0)1684 895767
> Long Range Ground Radar Sensors Fax. +44 (0)1684 896315
> LSC2 Division Email.
PEHOWLAND at DRA.HMG.GB
> Defence Research Agency
> St Andrews Road
> Malvern
> Worcestershire, WR14 3PS, UK
>
=========================================================================
Try this.
janus> math
Mathematica 2.2 for NeXT
Copyright 1988-93 Wolfram Research, Inc.
-- NeXT graphics initialized --
In[1]:= MyPartition[list1_, list2_] :=
Map[ Take[ list1, #]&,
FoldList[ Plus, {1, First[list2]}, Partition[list2, 2, 1]
]
]
In[2]:= MyPartition[{A,B,C,D,E,F,G,H,I,J}, {2,3,4,1}]
Out[2]= {{A, B}, {C, D, E}, {F, G, H, I}, {J}}