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help for selectvars
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Selecting all possible n-tuples from a varlist 

        selectvars varlist [, min(#) max(#) ]


Description

    selectvars produces a list of all possible n-tuples from a list of
    variable names. That is, given a list of k variable names, it produces
    the empty list; all possible distinct singletons (each individual
    variable name); all possible distinct pairs; and so forth. Tuples are
    bound in " ". As selectvars is intended for programming, the list is not
    displayed, but left behind as a saved result.

    Note that there is no checking of a possible error with even modest k:
    that a full list of (at most 2^k) tuples can not be accommodated in a
    macro.

    As of January 2011, this command is declared superseded by the author's
    tuples.


Options 

    min(#) specifies a minimum value for the number of names in a tuple.

    max(#) specifies a maximum value for the number of names in a tuple.


Examples

    . selectvars headroom trunk length displacement

    . foreach v in `r(varlist)' {
    .        regress mpg `v'
    . }
    
    . selectvars headroom trunk length displacement, min(2) max(2)


Saved results 

    r(varlist)        list of tuples


Author

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


Acknowledgments 

    Sebastian Orbe reported a problem in tuples which led to a bug fix.