Re: Sort problem

[Michel Machado <michel@...>]

Dears,

  I think that this comment could be added to the Lua manual.

  Thanks Aaron!

[ ]'s
Michel Machado

On Mon, 2004-07-26 at 14:45, Aaron Brown wrote:
> Michel Machado wrote:
> 
> > table.sort(t,
> >   function (a, b)
> >     assert(a ~= nil, "left var is nil!")
> >     assert(b ~= nil, "right var is nil!")
> >     return not (a < b) -- I want an inverted sort!
> >   end)
> 
> I've done this exact same thing.  The reference manual says:
> 
> # If comp is given, then it must be a function that receives
> # two table elements, and returns true when the first is
> # less than the second (so that not comp(a[i+1],a[i]) will
> # be true after the sort).
> 
> A not-so-obvious corollary is that the function has to
> return false if the two items are equal.  The sort algorithm
> depends on this being true and does weird stuff if it's not
> true.  Instead use "return a > b" as suggested by Virgil
> Smith.
> 
> (And don't feel bad -- it took me a couple days to figure
> this out when it happened to me.)