Using value labels in expression to modify value labels

[Momar Dieng]

Hello,
I would like to modify value labels of a variable when I know the labels but not necessarily the underlying values to which they correspond. In my case the underlying value is not important and may change, and the code should be agnostic to this. Based on Stata Tip 14: "Using value labels in expressions", I hoped something like this would work:

label define gender "F":gender "Girls", modify

where I expect the piece "F":gender to return the value that F is a label for, and the command as a whole would then relabel F to Girls. But this does not work and Stata complains that I'm using "invalid syntax". What am I missing or how else could this be done?

Best regards,


Momar

[Nick Cox]

The solution is different, but first note that the help for label defines legal syntax:

label define lblname # "label" [# "label"...] [, add modify replace nofix]

With only very occasional exceptions, whatever isn't explicitly permitted is forbidden. Your fantasy syntax is illegal, as you found out. With this much known, there are various ways to proceed. but perhaps the easiest is

decode gender, gen(sex)
replace sex = "Girls" if sex == "F"
encode sex, gen(gender2)

A merit of that approach is that it changes only what you see changed. Changing value labels can be tricky, as you need to watch out for side-effects.

Although I have not used any here, many ways of looking up things are documented under help extended fcn

For that matter, describe and label list would tell you what corresponds to what.

[daniel klein]

The key point here is the word expression. You need to evaluate that expression.

label define `= gender "F":gender' "Girls", modify

should work fine.

Also see labvalch3 as a part of labutil2 from the SSC.

and code e.g.

labvalch3 gender ,subst("F" "Girls")

Best
Daniel

[Momar Dieng]

Thanks both Nick and Daniel for the very pedagogical solutions!

[Momar Dieng]

Just for posterity there is a small typo in Daniel's solution. This is what worked for me:

label define gender `="F":gender' "Girls", modify

Thanks again.

[daniel klein]

You are right. I omitted the value label name, thanks for spotting this. Should be

label define lblname `= "label":lblname' "new label" ,modify

Best
Daniel