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help for ^swor^                                                    (STB-59: dm86)
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Draw random sample (alternative to ^sample^) 
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	^swor^ # [^if^ exp] [^in^ range] [^,^ ^by(^groupvars^)^ ^g^enerate^(^newvar^)^ 
    	         ^k^eep ]


Description
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^swor^ draws a pseudo-random sample of size # from the data in memory, by 
default discarding (optionally keeping) the remaining observations.  
Observations not meeting the optional ^if^ and ^in^ criteria are kept 
(sampled at 100%). # must be positive and no greater than the number of 
observations in each group to be sampled.

Sampling here is defined as drawing observations without replacement.  
See help on @sample@ for sampling without replacement specified in percent 
to be sampled, rather than absolute number. See help on @bstrap@ for 
sampling with replacement.
 
If you are serious about drawing random samples, you must first set the 
random number seed; see help @generate@.


Options
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^by(^groupvars^)^ specifies that a sample of size # is to be drawn within each 
    set of values of groupvars.

^generate(^newvar^)^ generates newvar containing 1 for those observations 
    included in the sample and 0 for those not included.

^keep^ overrides the default dropping of nonsampled observations. ^keep^ 
    must be combined with ^generate( )^. 


Examples
--------

    draw sample of 100: 	
    . ^swor 100^                        
 
    keep all ^sex^ != 0, but sample 100 from ^sex^ == 0: 
    . ^swor 100 if sex == 0^                 
   
    sample 100 from each group of ^sex^: 
    . ^swor 100, by(sex)^            

    sample 100 from each group of ^sex^, but keep all observations: 
    . ^swor 100, by(sex) gen(sample) keep^
    
    sample 100 if ^sex^ == 0 and keep only those observations:
    . ^swor 100 if sex == 0, gen(sample)^ 
    . ^keep if sample^ 


Author
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         Nicholas J. Cox, University of Durham, U.K.
         n.j.cox@@durham.ac.uk


Also see
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 Manual:  ^[R] sample^
On-line:  help for @sample@, @bstrap@