Re: [Slib-discuss] subarray to access diagonals

[Aubrey Jaffer]

 | Date: Tue, 24 Jun 2008 19:57:54 +0800
 | From: "Fernan Bolando" <address@hidden>
 | 
 | Is there a direct way to access the diagonal of an array using
 | subarray.  My limited scheme abilities seem to prevent me from
 | understanding the documentation directly.

Not using the subarray procedure, but using "make-shared-array":

  http://swiss.csail.mit.edu/~jaffer/slib_7.html#SEC193

  Function: make-shared-array array mapper k1 ...

    make-shared-array can be used to create shared subarrays of other
    arrays.  The mapper is a function that translates coordinates in
    the new array into coordinates in the old array.  A mapper must be
    linear, and its range must stay within the bounds of the old
    array, but it can be otherwise arbitrary.  A simple example:

    (define fred (make-array '#(#f) 8 8))
    (define freds-diagonal
      (make-shared-array fred (lambda (i) (list i i)) 8))
    (array-set! freds-diagonal 'foo 3)
    (array-ref fred 3 3)   ==> foo