Hi Pierre,

Does matrix-map-cols do what you want?  It's the last function on page
https://docs.racket-lang.org/math/matrix_poly.html

Also, welcome to Racket!

Dave


On Mon, Oct 17, 2016 at 7:00 PM, Pierre-Henry Frohring <
frohring.pierrehe...@gmail.com> wrote:

> Hello,
>
> First time here, and just a few hours into Racket...
> It is not going to be rocket science ;-).
>
>
> Context:
>
>   I am using Emacs and org-mode to map each heading of an org file to a
> html file.
>   Result: one org file → one static website.
>     https://github.com/phfrohring/org-to-blog
>
>   The org file contains data that is exported to a tsv file:
>     https://github.com/phfrohring/org-to-blog/blob/master/test/
> blog.org#data
>
>   A code block in the org file is evaluated:
>     https://github.com/phfrohring/org-to-blog/blob/master/test/
> blog.org#processing
>
>   And produces a stacked-chart from the tsv data:
>     https://github.com/phfrohring/org-to-blog/blob/master/test/
> blog.org#result
>
>
> The tsv data is parsed into a kind of matrix `M` where each cell `M[i][j]`
> is a
> string.
>   ex: `M[i][0]` is the column "day" i.e. contains dates
>       `M[i][1]` is the column "description" i.e. contains strings
>
> In order to use operations over "day" column (adding dates, ...) it is
> needed to
> parse that column with something like: `iso8601->date` but not the
> "description"
> column.
>
> So, it is needed to apply a vector of functions `vF = [f_0,f_1,...]` to `M
> =
> [col_0,col_1,...]` such that: `(matrix-apply vF M) = M'` where:
>
>                 M' = [f_0(col_0),f_1(col_1),...,f_n(col_n)]
>
> Well, this function `matrix-apply` does not seem to exist and my attempt at
> implementing it feels clunky to say the least (ex: fs is not a vector):
>
>     (define (matrix-apply fs m)
>       (cond [(= (length fs) (matrix-num-cols m))
>              (matrix-augment
>               (map (λ (f_col)
>                      (apply
>                       (λ (mat) (matrix-map (car f_col) mat))
>                       (cdr f_col)))
>                    (zip
>                     fs
>                     (matrix-cols m2))))]
>             [#t (error fs)]))
>
>     (define m2 (matrix [[1 2 3 4]
>                         [1 2 3 4]]))
>
>     (matrix-apply (list sqr sqr sqr sqr) m2)
>
>     => (array #[#[1 4 9 16] #[1 4 9 16]])
>
>
> Am I missing the elephant in the corridor? Is an implementation floating
> somewhere?
>
> Thx!
>
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