Re: PL/pgsql function handle CUBE values

Rajarshi Guha wrote:
> Hi, I am trying to write a PL/pgsql function that will take a CUBE
> variable (which will be a 1D point) and a double precision variable.
>
> If the input CUBE is defined as
>
> '(x,y,z)'::cube
>
> the function would then return a CUBE value of the form
>
> '(x+R,y+R,z+R),(x-R,y-R,z-R)'::cube
>
> where R is the second argument.
>
> The problem I'm having is to actually add R to the individual components
> of the CUBE variable. I can't cast CUBE to float[] and I don't see
> anyway to get at the individual components of the CUBE.

I haven't tested this, but it looks like you can use cube_subset() to do
that.

 From [0]:

   cube_subset(cube, int[]) returns cube

   Makes a new cube from an existing cube, using a list of dimension
   indexes from an array. Can be used to find both the LL and UR
   coordinates of a single dimension, e.g.
   cube_subset(cube('(1,3,5),(6,7,8)'), ARRAY[2]) = '(3),(7)'. Or can be
   used to drop dimensions, or reorder them as desired, e.g.
   cube_subset(cube('(1,3,5),(6,7,8)'), ARRAY[3,2,1,1]) = '(5, 3, 1,
   1),(8, 7, 6, 6)'.

For each dimension, select cube_subset(your_cube, ARRAY[dimension]) and
then increment or decrement by R.

Further, it looks like you're actually trying to create a function that
will do precisely what cube_enlarge() does.

Also from [0]:

   cube_enlarge(cube c, double r, int n) returns cube

   Increases the size of a cube by a specified radius in at least n
   dimensions. If the radius is negative the cube is shrunk instead. This
   is useful for creating bounding boxes around a point for searching for
   nearby points. All defined dimensions are changed by the radius r. LL
   coordinates are decreased by r and UR coordinates are increased by r.
   If a LL coordinate is increased to larger than the corresponding UR
   coordinate (this can only happen when r < 0) than both coordinates are
   set to their average. If n is greater than the number of defined
   dimensions and the cube is being increased (r >= 0) then 0 is used as
   the base for the extra coordinates.

Colin

[0] http://developer.postgresql.org/pgdocs/postgres/cube.html