Re: Getting rid of those deprecated Do[] loops?
- To: mathgroup at smc.vnet.net
- Subject: [mg92772] Re: Getting rid of those deprecated Do[] loops?
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Mon, 13 Oct 2008 06:16:43 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <gcsctj$8mj$1@smc.vnet.net>
AES wrote:
> Trying to think of a "two-variable iterator" approach that will let one
> produce the same results as
>
> data = { };
> Do[
> Do[
> data = AppendTo[data, {aa, bb, xx, yy}],
> {bb, 10, 30, 10}],
> {aa, 1, 2}];
> Print[data // TableForm];
>
> without using those universally deprecated (and even worse, nested)
> Do[ ] loops, not to mention the equally deprecated AppendTo[].
>
> Somewhat to my surprise, the construction
>
> Table[{aa = kk[[1]]; bb = kk[[2]]; aa, bb, xx, yy},
> {kk, {{1, 10}, {1, 20}, {1, 30}, {2, 10}, {2, 20},
> {2,30}}}
> ] // TableForm
>
> using a two-dimensional iterator iterator variable kk, actually does
> this, though the "iterator list" is obviously a bit messy.
>
> Simpler way of defining an iterator to do this? In more than two
> iterator dimensions (aa, bb, cc,...)? (with no functional dependence
> between the values of aa, bb, cc).
>
> Is the concept of a multi-dimensional iterator variable kk mentioned in
> the M6 documentation anywhere? (A search on "Iterate" or "iteration"
> brings up 193 hits at 10 per screen.)
(* Compare the order of the iterators in *)
Flatten[
Table[{aa, bb, xx, yy}, {aa, 1, 2}, {bb, 10, 30, 10}], 1]
{{1, 10, xx, yy}, {1, 20, xx, yy}, {1, 30, xx, yy}, {2, 10,
xx, yy}, {2, 20, xx, yy}, {2, 30, xx, yy}}
(* versus *)
data = {};
Do[Do[data = AppendTo[data, {aa, bb, xx, yy}], {bb, 10, 30, 10}], {aa,
1, 2}]
data
{{1, 10, xx, yy}, {1, 20, xx, yy}, {1, 30, xx, yy}, {2, 10,
xx, yy}, {2, 20, xx, yy}, {2, 30, xx, yy}}
Regards,
-- Jean-Marc