Re: A better way to decimate a file??

• To: mathgroup at smc.vnet.net
• Subject: [mg21359] Re: A better way to decimate a file??
• From: Tobias Oed <tobias at physics.odu.edu>
• Date: Wed, 29 Dec 1999 14:15:45 -0500 (EST)
• Organization: Old Dominion University
• References: <849j3v\$pgm@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Rob Peterson wrote:
>
> I start with a list y that I need to decimate (sp?).  I've looked thru
> the book and the only list function I can find to dump list elements
> is the Drop[] function.  But, the best I can do is get rid of half of
> the elements at a time.  I want to decimate this list by 16, ie I want
> to dump 15 of every 16 entries.  So, I dump half of them four times.
> This seems to work but I figure the pros hanging in this group will
> know a much more elegant way to do this.  I did this:
>
> (* start with y as the list  and ly = Length[y]  *)
>
> y2 = Drop[y, {1, ly, 2}]; ly2 = Length[y2]
>
> y4 = Drop[y2, {1, ly2, 2}]; ly4 = Length[y4]
>
> and so on
>
> So how should it really be done?  I'd like to be able to decimate by
> non-binary numbers too.
>
> Thanks, Rob

I think this is what you want,

ly=50

y=Table[i,{i,ly}] (* build an example list *)

Map[First,Partition[y,16]]

This will give you elements 1,17 and 33 of y.
Tobias

```

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