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Re: AW: st: random draw of single variable, not whole data


From   Jeph Herrin <junk@spandrel.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: AW: st: random draw of single variable, not whole data
Date   Thu, 26 Feb 2009 14:41:29 -0500


You're right about the missings; I didn't get any but
I could have. Maybe

   gen y = x[ceil(_N*uniform())]

as long as uniform() never returns precisely 0, which I've
never seen - can it?

But certainly there's no reference to the values that x takes;
a random observation number is generated in (1,...,_N) and y is
set equal to that observation on x. So yes, it handles whatever
x looks like, I'm merely sampling from the list of observation
numbers.

J




Martin Weiss wrote:
<>

Your "with replacement" method leads to missings every now and then. Apart
from that, if Florian had an irregularly spaced list of numbers to sample
from, which also need not be integers, would your method be capable of
handling that?



HTH
Martin


-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Jeph Herrin
Gesendet: Donnerstag, 26. Februar 2009 20:20
An: statalist@hsphsun2.harvard.edu
Betreff: Re: st: random draw of single variable, not whole data


It's not clear if you want sampling with or without replacement.

With replacement:

   gen y = x[round(_N*uniform(),1)+1]

without replacement:

   egen index=rank(uniform())
   gen y = x[index]

hth,
Jeph


Florian Wakolbinger wrote:
Dear all,

is it possible to randomly draw numbers out of a variable x and write it into another variable y

i.e. if

x
1
2
3
4
5

then y could be, for instance

y
3
5
3
2
4

all numbers in y are randomly drawn from x. how is it possible to construct such a variable y in stata?

thanks, and kind regards
florian

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