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Re: Do-command

• To: mathgroup at smc.vnet.net
• Subject: [mg102647] Re: [mg102588] Do-command
• From: Leonid Shifrin <lshifr at gmail.com>
• Date: Mon, 17 Aug 2009 04:31:46 -0400 (EDT)
• References: <200908161038.GAA01118@smc.vnet.net>

Hi Uwe,

Do is not supposed to produce any output by itself (it produces Null).
You should either use side effects (assignments) to save your results,
or use a different programming style (such as functional programming).
You can also use Reap and Sow.
If I understand correctly what you really want, it can be achieved by

In[1] = Map[Function[x, Select[{1, 2, 4, 7, 6, 2}, # >= x &]], Range[7]]

Out[1] = {{1, 2, 4, 7, 6, 2}, {2, 4, 7, 6, 2}, {4, 7, 6}, {4, 7, 6}, {7,
  6}, {7, 6}, {7}}

With Reap and Sow, you will get it in this way:

In[2] = Reap[Do[Sow[Select[{1, 2, 4, 7, 6, 2}, # >= i &]], {i, 7}]][[2, 1]]

Out[2] = {{1, 2, 4, 7, 6, 2}, {2, 4, 7, 6, 2}, {4, 7, 6}, {4, 7, 6}, {7,
  6}, {7, 6}, {7}}


Regards,
Leonid


On Sun, Aug 16, 2009 at 2:38 PM, Uwe Gotzes <u.gotzes at googlemail.com> wrote:

> Hi!
>
> Can anybody tell, why
> Do[Select[{1, 2, 4, 7, 6, 2}, # >= i &], {i, 7}]
> does not produce output in Mathematica?
>
>

• References:
  • Do-command
    • From: Uwe Gotzes <u.gotzes@googlemail.com>