.-
help for ^genl^, ^repl^, ^redo^, ^defntion^             
                               Jeroen Weesie & Albert Verbeek/ICS  Jan 03, 1997
.-

Defined variables with automatic variable labels                [STB-35: dm43] 
------------------------------------------------

        ^genl^ [type] newvar ^=^ exp [^if^ exp] [^in^ range] [^,^ 
                                ^by(^varlist^) l^abel^(^str^)^ ^nod^ef ]

        ^repl^ oldvar ^=^ exp [^if^ exp] [^in^ range] [^,^ 
                                ^by(^varlist^) l^abel^(^str^)^ ^o^ldlabel ^nod^ef ]

        ^redo^ varlist

        ^defntion^ [varlist] [, ^o^ther]


Description
-----------

^genl^ and ^repl^ are enhancements of Stata's commands ^generate^ and ^replace^.
  - the definition for a variable is saved as the characteristic ^Defntion^ 
    associated with that variable. Thus, definitions of variables are saved 
    along with your data!  The definition comprises the defining expression, 
    the case restrictions -if- and -in-, and the -by varlist- clause. 
  - ^genl^ and ^repl^ use the defining expression to label the variable. So you 
    record how the variable was constructed. If the expression is too long, 
    the label is truncated and "..." is added. 

^redo^ uses the characteristic ^Defntion^ to redefine the variables in the order 
implied by varlist. With some inspiration (and additional respiration), a poor 
man's spreadsheet can be constructed.

^defntion^ displays the definitions of the variables. 


Options
-------

^label(^string^)^ specifies the label of the variable instead of the defining 
   expression. Specify ^label(_)^ to force an empty label. Specifying a label
   not does affect the definition of the charactistic Defntion.

^nodef^ suppresses the generation (^genl^) or modification (^repl^) of the 
   characteristic Defntion.

^oldlabel^ specifies that the label of the variable should not be changed.

^by(^varlist^)^ specifies that the expression should be evaluated "by varlist:".
   The sort order of the variables is changed only if needed.

^other^ specifies that ^defntion^ includes variables without a definition. 


Examples
--------

   . ^genl age = Tnow - Tbirth^       creates age with label "D: Tnow - TBirth"
   . ^genl N = invnorm(uniform())^                     creates a normal variate
   . ^genl M = N^^2+N+1, label(own label)^                      supply own label
   . ^defntion^                                      list the defined-variables

Since ^N^ is defined using (pseudo-)random number, re-evaluating the expression 
generates new values for ^N^,

   . ^redo N^
     
Note though that the variable ^M^ was defined in terms of ^N^. Since ^genl^ stored
the definition of ^M^, it is possibly to update ^M^ 

   .^ redo M^
     
Since variables are updated in the specified order, it would have been easier 
to have issued the command 

   . ^redo N M^         redraw a normal variate for ^N^, and update ^M^ accordingly


Acknowledgement
---------------  

The commands ^genl^, ^repl^, ^redo^, and ^defntion^ are extensive updates of early 
versions in the ETS-Kit, a collection of Stata programs written for Stata 2.1 
by the late Albert Verbeek and Jeroen Weesie. 


See also
--------

    STB:  dm43 (STB-35)
 Manual:  [R] generate
          [R] label
On-line:  help for @generate@, @replace@, @char@