Building up larger matrices a la Matlab in core.matrix

[László Török]

Hi,

I've started using core.matrix as I've been missing the power of Matlab in my daily clojure work. It has been a fantastic experience so far.

However, I've been missing the elegant and succinct way to combine smaller matrices into larger ones a la Matlab.

I tried

(join

  [1 2]

  (slices [[3 4] 

              [5 6]])

  [7 8])

which is a bit more verbose than I wanted to, plus it complains about dim. mismatch. That goes away, if I do (join (concat ...)).

Ideally, I would want to do

(some-clever-join-op [[A B]

                                   [C D]])

and get a matrix that is a combined result of A-D matrices glued together along those dimensions. 

Is there already an elegant way of doing this in core matrix?

Thanks!

Laszlo

[Mike Anderson]

On Thursday, 8 January 2015 02:18:37 UTC+8, László Török wrote:

Hi,

I've started using core.matrix as I've been missing the power of Matlab in my daily clojure work. It has been a fantastic experience so far.

However, I've been missing the elegant and succinct way to combine smaller matrices into larger ones a la Matlab.

I tried

(join

  [1 2]

  (slices [[3 4] 

              [5 6]])

  [7 8])

which is a bit more verbose than I wanted to, plus it complains about dim. mismatch. That goes away, if I do (join (concat ...)).

join is the right thing to use: the reason it doesn't work here is that you are joining a vector to a sequences of vectors and then to another vector. "join" recognises that the sequence of vectors is a mismatch, hence the error.

Ideally, I would want to do

(some-clever-join-op [[A B]

                                   [C D]])

and get a matrix that is a combined result of A-D matrices glued together along those dimensions. 

Is there already an elegant way of doing this in core matrix?

You can do something like:

(defn join-all

     "Joins a matrix of matrices to create a bigger matrix :-)"

     ([M]

       (apply join (map #(apply join-along 1 %) (slices M))))) 

I think this does what you want?

(join-all [[ [[1]] [[2 3]]]

              [ [[4] [7]] [[5 6] [8 9]]]])

=> [[1 2 3] [4 5 6] [7 8 9]]

[László Török]

Hi, 

thanks! For some reason, I did not get email updates delivered to my inbox, but I ended up doing sg similar:

(defn join-all [m-of-m]

  (apply m/join

         (for [row m-of-m]

           (apply m/join-along (cons 1 row)))))

thx

Las

[Mike Anderson]

Yep that should work....though you are making the (slightly) risky assumption that m-of-m is seqable, which not all implementations are.

For safety, it is best to use "slices" if you want to turn a matrix into a seq of its rows.....

[László Török]

Good catch, thanks for pointing out!

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