Re: filter an array in place

[Matthew Wild <mwild1@...>]

On 14 January 2011 04:30, Drake Wilson <drake@begriffli.ch> wrote:
> Quoth Emmanuel Oga <emmanueloga@gmail.com>, on 2011-01-14 01:12:40 -0300:
>> Is there any other more elegant way?
>
> There's not much that's "elegant" in the sense of "easy using the Lua
> table library" or such, that I can see.  If I were coding it all the
> way down, I'd do something like this:
>
>    function filtern(t, predicate)
>       local j = 1
>
>       for i, v in ipairs(t) do
>          if predicate(v) then
>             t[j] = v
>             j = j + 1
>          end
>       end
>
>       while t[j] ~= nil do
>          t[j] = nil
>          j = j + 1
>       end
>
>       return t
>    end
>

Similar to some (slightly more generic) code I wrote:
http://hg.prosody.im/trunk/file/339b909c15a0/util/array.lua#l35

OT but perhaps interesting: array_base in that module is a nice hack I
came up with to have the ability to choose whether an operation should
mutate an array or not. array.filter(myarray, is_prime) returns a new
filtered array, while myarray:filter(is_prime) modifies myarray
in-place. Both use array_base.filter().

Regards,
Matthew