I am implementing A* for http://aichallenge.org/specification.php and was wondering a slick way to select the minimum of a collection based of the schartzian transform.
Basically, I have a collection of suitable squares to move to, and I want to move to the square with the lowest cost.
Basically I will be selecting the square from my neighbors who has the lowest cost in a loop.
The only way I can think to do this is with something like
next_spot = spot.neighbors.sort_by |a,b| { a.cost(dest) <=> b.cost(dest) }.first
But I would really like something higher performance, because I don't really want to sort the collection, I just want the one with the minimum transform value
Note, I could write something more verbose and "C-style" looping and keeping track of a previous minimum, but I was hoping for something clear and compact.
Why not use min_by?
next_spot = spot.neighbors.min_by { |x| x.cost(dest) }
And if a "_by" version of an Enumerable-ish method doesn't exist you can get old school and do the Schwartzian Transform by hand with this sort of pseudo-Ruby pattern:
a.map { |x| [ expensive(x), x ] }. # Do the expensive part once and cache it
op { |x| something_with x.first... }. # Do what you really came to do
map { |x| x.last } # Unwrap the caching