Re: loops?

• To: mathgroup at smc.vnet.net
• Subject: [mg92814] Re: loops?
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Tue, 14 Oct 2008 04:56:02 -0400 (EDT)
• References: <gcv784\$dsn\$1@smc.vnet.net>

```Bob Hanlon wrote:
> n = 100; m = 100;
>
> data1 = {};
> Timing[Do[
>    Do[data1 = AppendTo[data1, {aa, bb, xx, yy}], {bb, 10, m,
>      10}], {aa, 1, n}];]
>
> {0.03825,Null}
>
> Timing[data2 =
>    Table[{aa = kk[[1]]; bb = kk[[2]]; aa, bb, xx, yy}, {kk,
>      Flatten[Outer[{#1, #2} &, Range[n], Range[10, m, 10]], 1]}];]
>
> {0.003871,Null}
>
> Timing[data3 =
>    Flatten[Outer[{#1, #2, xx, yy} &, Range[n], Range[10, m, 10]],
>     1];]
>
> {0.00092,Null}
>
> data1 == data2 == data3
>
> True
>
>
> Bob Hanlon
>
> ---- AES <siegman at stanford.edu> 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.)
>
>
> --
>
> Bob Hanlon
>
>
A quick comment on the above - never time any process for less than (at
least) a few seconds - otherwise the result is meaningless.

This is not aimed at you, Bob, but at the original author of the question.

David Bailey
http://www.dbaileyconsultancy.co.uk

```

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