On 09.01.2010, at 21:22, Rock wrote:
I'm working on implementing a solution for extracting slices of
multidimensional vectors, in the sense of vectors of vectors. I'm
taking the recursive route.
I have some code for working with nested vectors here:
http://code.google.com/p/clj-multiarray/source/browse/src/clj_multiarray/nested_vectors.clj
It's work in progress, but it may give you some ideas.
Anyway, I'm trying to follow the MATLAB path. For instance, suppose
this is a 5x5 matrix:
(def a [[2 3 5 7 11] [13 17 19 23 29] [31 37 41 43 47] [53 59 61
67 71] [73 79 83 89 97]])
This:
(submvec a [[0 2 4] [0 2 4]])
would yield:
[[2 5 11] [13 19 29] [31 41 47] [53 61 71] [73 83 97]] (actually a
sequence)
In other words, [0 2 4] is to be interpreted as [START STRIDE END].
STRIDE should be optional.
That's my "sample" function:
(defn nv-sample
[x dim start end step]
(assert (vector? x))
(if (zero? dim)
(vec (take-nth step (subvec x start end)))
(vec (map #(nv-sample % (dec dim) start end step) x))))
Just call it once for each dimension (0 and 1).
Konrad.
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