Re: filter an array in place

["Robert G. Jakabosky" <bobby@...>]

On Thursday 13, Emmanuel Oga wrote:
> Hello, I'm looking for the best proper way of doing this:
>
> local tab = {"a", "a", "c", "a", "d", "a" }
>
> for index, val in ipairs(tab) do
>   if val == "a" then -- could be any other complex condition
>     table.remove(tab, index)
>   end
> end
>
> -- WRONG: tab = { "a", "c", "d" }, should be { "c", "d" }
>
> So removing elements from a container _while you are iterating it_ is
> wrong in most languages. I'm looking for the nicest and proper way of
> doing it.
>
> Two methods I came up with:
>
> 1) popping from the array and pushing to a new one if the condition is met.
> 2) Iterating first, storing indexes to remove, then removing one by
> one (compensating index offset as a result of each removed elements)
>
> http://pastie.org/1458808
>
> Is there any other more elegant way?

process the list in reverse.

for index=#tab,1,-1 do
  local var = tab[index]
   if val == "a" then -- could be any other complex condition
     table.remove(tab, index)
   end
end


-- 
Robert G. Jakabosky