I will point out again that sampling a five-fold replicate of 1:20 is not
the same as resampling with replacement, although I made an error in
reporting probabilities - the P(x2 = 1 | x1 = 1) = 4/99 and not 4/100.
When sampling with replacement, P(x2 = 1 | x1 = 1) = P(x2 = 1 | x1 != 1) =
1/20.
--------------------------------------
Jonathan P. Daily
Technician - USGS Leetown Science Center
11649 Leetown Road
Kearneysville WV, 25430
(304) 724-4480
"Is the room still a room when its empty? Does the room,
the thing itself have purpose? Or do we, what's the word... imbue it."
- Jubal Early, Firefly
r-help-boun...@r-project.org wrote on 03/02/2011 01:05:01 PM:
> [image removed]
>
> Re: [R] bootstrap resampling - simplified
>
> Vokey, John
>
> to:
>
> r-help
>
> 03/02/2011 01:07 PM
>
> Sent by:
>
> r-help-boun...@r-project.org
>
> On 2011-03-02, at 4:00 AM, r-help-requ...@r-project.org wrote:
>
> > Hello there,
> >
> > I have a problem concerning bootstrapping in R - especially
> focusing on the resampling part of it. I try to sum it up in a
> simplified way so that I would not confuse anybody.
> >
> > I have a small database consisting of 20 observations (basically
> numbers from 1 to 20, I mean: 1, 2, 3, 4, 5, ... 18, 19, 20).
> >
> > I would like to resample this database many times for the
> bootstrap process with the following conditions. Firstly, every
> resampled database should also include 20 observations. Secondly,
> when selecting a number from the above-mentioned 20 numbers, you can
> do this selection with replacement. The difficult part comes now:
> one number can be selected only maximum 5 times. In order to make
> this clear I show you a couple of examples. So the resampled
> databases might be like the following ones:
> >
> > (1st database) 1,2,1,2,1,2,1,2,1,2,3,3,3,3,3,4,4,4,4,4
> > 4 different numbers are chosen (1, 2, 3, 4), each selected - for
> the maximum possible - 5 times.
> >
> > (2nd database) 1,8,8,6,8,8,8,2,3,4,5,6,6,6,6,7,19,1,1,1
> > Two numbers - 8 and 6 - selected 5 times (the maximum possible
> times), number 1 selected 4 times, the others selected less than 4
times.
> >
> > (3rd database) 1,1,2,2,3,3,4,4,9,9,9,10,10,13,10,9,3,9,2,1
> > Number 9 chosen for the maximum possible 5 times, number 10, 3, 2,
> 1 chosen for 3 times, number 4 selected twice and number 13 selectedonly
once.
> >
> > ...
> >
> > Anybody knows how to implement my "tricky" condition into one of
> the R functions - that one number can be selected only 5 times at
> most? Are 'boot' and 'bootstrap' packages capable of managing this?
> I guess they are, I just couldn't figure it out yet...
> >
> > Thanks very much! Best regards,
> > Laszlo Bodnar
>
> Laszlo,
> Create a vector consisting of 5 of each number. Then, for each
> sample, scramble the order of the items in the vector, and select
> the first 20.
>
>
> --
> Please avoid sending me Word or PowerPoint attachments.
> See <http://www.gnu.org/philosophy/no-word-attachments.html>
>
> -Dr. John R. Vokey
>
> ______________________________________________
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> PLEASE do read the posting guide
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