— Function: grid:map-n-grids &key sources destination destination-affi destination-specification initial-element element-functions combination-function combine-destination

Map on multiple source grids. The arguments are: sources: A list of (grid-or-function affi), each one representing either a grid or function from which data will be drawn. If it is a grid, the grid values are used. If it is a function of the appropriate number of non-negative integer arguments, values will be created by calling that function on the indices. If affi is not specified and grid-or-function is a grid, the affi will default to the affi of that grid.

destination:

A grid in which to put the results, or nil if one is to be created.

destination-affi:

An affi for the destinattion.

destination-specification:

A specification for the destination, if destination-affi is not given.

initial-element: Initial value to give to the destination grid.

element-functions:

A list of functions or nil, one for each source. This function is applied to the source element before combination.

combination-function:

A function that combines each of the source values after being passed through the element-functions. If nil, then just take the value from the first source.

combine-destination:

If true, pass as the first argument to the combination-function the prior value of the destination grid. Defaults to t if :desination is specified; otherwise nil.

     (map-n-grids :sources `((,#31m(1 2 3) nil) (,#31m(9 8 7) nil))
                  :combination-function (lambda (a b) (+ a (* 2 b))))