st: Re: value labels for string variables

[baum <baum@bc.edu>]

--On Sunday, October 27, 2002 2:33 -0500 Richard wrote:

> SAS, SPSS. and S-Plus allow value labels for string variables. Also they
> allow the development of value labels independent of the database being
> value labeled. (Proc Format)
>
> STATA does not, at least not without some (considerable) rigamorrole.
>
> Maybe Stata people will fix this.
>
> At present the soltuion (that is quickest)  seems to be  developing a new
> variable using the valkue label as a variable value. This is not
> database-wise efficient. And these labels are not easily reduced to short
> strings; subtle disease distinctions are difficult to reduce to a few
> characters.
I don't see the issue here. Say that you have a million records, and one 
string variable recorded therein is str2 state, AK..WY [DC PR]. You do not 
want to store the 'long name' of the state in the database, so you set up a 
new dataset with 50, 51 or 52 cases, containing str2 state. You encode 
state into int statename, and you define a value label containing 50, 51 or 
52 values for that integer variable, containing the long names of states.

If you then merge this dataset with your million-record dataset on state, 
statename will contain the 'value labels' of state, but will not store them 
as strings; it will store the integer value underlying. The overhead 
associated with this strategy is merely one integer per case (in the case 
of states, I could use a byte data type; in general an int will suffice). 
The following dataset appears to have long names for 'statename'; in 
reality it is an integer with a value label.

        state      var2      statename
 1.        MA       222  Massachusetts
 2.        MA       999  Massachusetts
 3.        MA       111  Massachusetts
 4.        ME       888          Maine
 5.        ME       333          Maine
 6.        NH       444  New Hampshire
 7.        NH       777  New Hampshire
 8.        VT       666        Vermont
 9.        VT       555        Vermont

It does not seem to me that this strategy is onerous, and it is only 
limited by the existing limits on labels. I do not imagine that the 
overhead involved can be improved upon in other packages' implementation of 
this feature; if you want to associate one of ~32K or ~64K string values 
with a case, you need an appropriately sized integer.

Kit

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