& sortby()
 
  Syntax: sortby([<obj>/]<attrib>,<list>[,<delimiter>])
 
  This function sorts an arbitrary list according to the u-function 
  <obj>/<attrib>.
 
  The u-function should compare two arbitrary elements, %0 and %1, and 
  return:
 
    * zero - if the elements are equal
    * a negative integer - if element 1 is less than element 2
    * a positive integer - if element 1 is greater than element 2. 
 
  A simple example, which imitates a normal alphabetic sort:
 
  > &ALPHASORT test=[comp(%0,%1)]
  > say [sortby(test/ALPHASORT,foo bar baz)]
  You say "bar baz foo"
 
  A slightly more complicated sort. #1 is "God", #2 is "Amby", "#3" is 
  "Bob":
 
  > &NAMESORT me=[comp(name(%0),name(%1))]
  > say [sortby(NAMESORT,#1 #2 #3)]
  You say "#2 #3 #1"
 
  Warning: The function invocation limit applies to this function.   	
  If this limit is exceeded, the function will fail _silently_. List   	
  and function sizes should be kept reasonable.
 
  See Also: sort()