Re: filter an array in place
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: Re: filter an array in place
- From: Miles Bader <miles@...>
- Date: 2011年1月14日 13:28:24 +0900
Emmanuel Oga <emmanueloga@gmail.com> writes:
> 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)
You don't actually have to store the indices to remove -- during the
first iteration, just set "deleted" entries to nil, and keep track of
the highest index. Then add a second pass that compacts the array
(using the stored index for the iteration bound, to avoid problems with
ipairs on non-proper arrays).
E.g. (untested):
local max_index = #ARRAY
local do_removals = false
-- first loop, set removed elements to nil
for i = 1, max_index do
if ARRAY[i] == "a" then
ARRAY[i] = nil
do_removals = true
end
end
-- second loop, compact array to remove holes
if do_removals then
local offset = 0
for i = 1, max_index do
if ARRAY[i] == nil then
offset = offset + 1
elseif offset ~= 0 then
ARRAY[i - offset] = ARRAY[i]
end
end
end
-miles
--
=====
(^o^;
(()))
*This is the cute octopus virus, please copy it into your sig so it can spread.