Re: [racket-users] a matrix question

[Tim Hanson]

Many thanks, Jens Axel! That looks very good and includes several techniques 
that will help and inspire me, in particular for*/matrix, which I hadn't used 
yet.

I'll try it out the next chance I get.

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Re: [racket-users] a matrix question

[Jens Axel Søgaard]

Hi Tim,

Here is one way to do it:

#lang typed/racket
(require math/matrix math/array)

(: columns->matrix (All (A) ((Listof (Matrix A)) -> (Matrix A
(define (columns->matrix cs)
  (define m (matrix-num-rows (first cs)))
  (define n (length cs))
  (: has-m-rows? : ((Matrix A) -> Boolean))
  (define (has-m-rows? c) (= (matrix-num-rows c) m))
  (unless (andmap has-m-rows? cs)
(error 'columns-matrix "all columns must have the same number of rows"))
  (for*/matrix n m ([c (in-list cs)]
[x (in-vector (matrix->vector c))]) : A
x))

(display (columns->matrix (list (col-matrix [1 2 3]) (col-matrix [4 5 6]

-- 
Jens Axel



2018-03-25 13:12 GMT+02:00 Tim Hanson :

> hi,
>
> I'm trying out matrices (without typed racket, though I read the
> performance caveat -- I'm not worried about performance at the moment) and
> am trying to find the best idioms for a small function I'd like to build.
>
> Q1: is there an elegant away to assemble a matrix column-wise? (my first
> draft solution is to read one col-matrix and write cell by cell into a
> destination (mutable) matrix); my preference would be to use immutable
> items, but that's secondary to elegance at this point.
>
> cheers,
>
> Tim
>
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-- 
-- 
Jens Axel Søgaard

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[racket-users] a matrix question

[Tim Hanson]

hi, 

I'm trying out matrices (without typed racket, though I read the performance 
caveat -- I'm not worried about performance at the moment) and am trying to 
find the best idioms for a small function I'd like to build.

Q1: is there an elegant away to assemble a matrix column-wise? (my first draft 
solution is to read one col-matrix and write cell by cell into a destination 
(mutable) matrix); my preference would be to use immutable items, but that's 
secondary to elegance at this point.

cheers,

Tim

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