; docformat = 'rst' ;+ ; Find the intersection of two sets of indices. A set of indices is ; represented by an array of non-negative integers where a scalar `-1L` ; indicates the empty set. ; ; :Examples: ; For example, try:: ; ; IDL> print, mg_setintersection([0, 3, 5, 6, 9], [3, 5, 7]) ; 3 5 ; ; :Returns: ; `lonarr` or `-1L` ; ; :Params: ; ind1 : in, required, type=lonarr or -1L ; array of indices where `-1L` indicates an empty set of indices ; ind2 : in, required, type=lonarr or -1L ; array of indices where `-1L` indicates an empty set of indices ; ; :Keywords: ; count : out, optional, type=long ; set to a named variable to return the number of elements in the ; intersection ;- function mg_setintersection, ind1, ind2, count=count compile_opt strictarr min12 = min(ind1, max=max1) > min(ind2, max=max2) max12 = max1 <; max2 ; if either set is empty or their ranges don't intersect results in an ; empty set if ((max12 lt min12) || (max12 lt 0L)) then begin count = 0L return, -1L endif r = where((histogram([ind1], min=min12, max=max12) ne 0L) and $ (histogram([ind2], min=min12, max=max12) ne 0L), count) return, count eq 0L ? -1L : (r + min12) end