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 <tbh...@gmail.com>:
> 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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