On Nov 4, 2007, at 3:41 PM, Terrence Brannon wrote:
i wrote a function to prepend unit axes onto an array. this is
oftentimes necessary to get arrays to the same rank before applying
some sort of operation to them.
if there is a better way to do this, I'm all ears. Please, no comments
about my parenthesizing style :)
(define prepend-unit-axes
(lambda (n a)
(if (= n 0)
a
(let* (
[ones (make-list n 1)]
[new-dim (flatten ones (array-dimensions a))]
[as-v (array-vector a)]
[as-l (vector-list as-v)]
)
(apply array '#() new-dim as-l)
Faster:
(use srfi-1)
(define (prepend-unit-axes cnt arr)
(if (positive? cnt)
(apply vector-array (array-vector arr)
arr ; Use same storage as source array
(append! (make-list cnt 1) (array-
dimensions arr)))
arr ) )
Even faster:
(define (prepend-unit-axes cnt arr)
(if (positive? cnt)
(apply make-shared-array arr
(lambda idxs (drop idxs cnt))
(append! (make-list cnt 1) (array-
dimensions arr)))
arr ) )
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Best Wishes,
Kon
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