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Re: transform Matrix and List elements toreplacement Rules

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113999] Re: transform Matrix and List elements toreplacement Rules
  • From: Thomas Dowling <thomasgdowling at gmail.com>
  • Date: Sat, 20 Nov 2010 06:13:24 -0500 (EST)

Hello,

A slightly different approach is to use Ordering to sort the matrix

matsorted = matrix[[Ordering[matrix]]]

Map[Thread[{a, b, c, d, e, f, g} -> #] &, matsorted[[1 ;; 4, 2 ;; 8]]]

I find that the Ordering approach is efficient especially with large
matrices, and may be easily
modified to sort by position.

For example, to sort by second-last position:

matrix[[Ordering[matrix[[All, -2]]]]]

Tom Dowling

On Fri, Nov 19, 2010 at 10:11 AM, leigh pascoe <leigh at evry.inserm.fr> wrote:

> I have a matrix that looks like this:
> matrix=
> {{1, 110, 120, 22, 64, 26, 24, 36, 390, 360, 1152},
>  {4, 21, 16, 30,  47, 23, 124, 127, 397, 367, 1152},
>  {2, 100, 103, 44, 71, 26, 81, 60,   302, 365, 1152},
> {3, 110, 165, 13, 55, 37, 27, 23, 363, 359, 1152}}
>
> I would like to sort it by the first element, delete the first and the
> last 3 columns and transform the remaining values  to Rules to give:
>
> {{a -> 110, b -> 120, c -> 22, d -> 64, e -> 26, f -> 24, g -> 36},
>  {a -> 100, b -> 103, c -> 44, d -> 71, e -> 26, f -> 81, g -> 60},
>  {a -> 110, b -> 165, c -> 13, d -> 55, e -> 37, f -> 27, g -> 23},
>  {a -> 21, b -> 16, c -> 30, d -> 47, e -> 23, f -> 124, g -> 127}}
>
> The idea is to then evaluate a formula using these sets of substitutions
> for a,b,..g. The actual matrix is of course larger than this one.
>
> There is no problem to sort and take the relevant parts
>
> sorted=Sort[matrix, #2[[1]] >= #1[[1]] &]
> data=sorted[[1;;4,2;;8]]
>
> However I can't find a way to transform the resulting List elements to
> replacement rules.
>
> I have tried creating a matrix with just the LHS of the rules:
>
> rules= Table["{a->,b->,c->,d->,e->,f->,g->}", {4}];
>
> and then to StringJoin the elements of matrix and rules. However I can't
> get this to work.
>
> I also tried generating the elements of the replacement matrix in a Perl
> program and importing it into Mathematica. This seemed to give the
> correct matrix, however it wouldn't actually work for the substitutions.
> It took me some time to realise that the matrix was in fact:
>
> data//FullForm
>
> List[List["a->110", "b->120", "c->22", "d->64", "e->26", "f->24",
> "g->36"],
>  List["a->0", "b->0", "c->0", "d->0", "e->2", "f->33", "g->63"],
>  List["a->0", "b->0", "c->2", "d->12", "e->5", "f->77", "g->86"],
>  List["a->113", "b->110", "c->27", "d->62", "e->18", "f->34",  "g->39"]]
>
> i.e. there are unwanted parentheses (that are not evident when FullForm
> is not specified). Can anyone help me to get the form that I want? Thanks.
>
> LP
>
>


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