RE: st: Generate random missing values within a set of variables

[Sofia Ramiro <sofiaramiro@hotmail.com>]

Thank you very much, Maarten!
Very useful and I can perfectly run it and adapt to my variables. 
I have been struggling during the last hours with how to adapt it when I want to generate missings randomly at 2 variables at the same time (and then 3 at the same time), etc. 
I tried thinking about finding a combination code. For example for the 2 variables missing, if I manage to set the random generation within the numbers 2, 3, 4, 5, 6, 8, 10, 12, 15 and 20, these could identify uniquely every combination (eg: 20 = 4*5, variables 4 and 5 missing). 
Do you think would be a good approach, or do you propsoe something better? And if this approach, how cna I generate random numbers within these numbers only?
Thank you very much!

Sofia

> Date: Sun, 15 Apr 2012 15:26:32 +0200
> Subject: Re: st: Generate random missing values within a set of variables
> From: maartenlbuis@gmail.com
> To: statalist@hsphsun2.harvard.edu
> 
> On Sun, Apr 15, 2012 at 2:06 PM, Sofia Ramiro wrote:
> > I have 6 variables (without missings) and I would like to randomly generate one missing value in one of the 6 variables per line/observation. I know that with the runiform command we manage to choose observations randomly within one variable (so I could generate random missing values within one variable), but how can I choose randomly one variable out of the 6 to be transformed into missing and make sure that one of them is being transformed per observation?
> 
> *---------- begin example ------------
> // create some data
> drop _all
> set obs 100
> forvalues i =1/6{
> 	gen x`i' = rnormal()
> }
> 
> // make a variable indicating
> // which variable will become missing
> gen tomis = ceil(6*runiform())
> 
> // turn for each observation the
> // appropriate variable to missing
> forvalues i = 1/6 {
> 	replace x`i' = . if tomis == `i'
> }
> 
> // see the result
> format x* %6.3g
> list in 1/10, clean
> *------------- end example -------------
> 
> Hope this helps,
> Maarten
> 
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
> 
> 
> http://www.maartenbuis.nl
> --------------------------
> 
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