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RE: st: AW: egen(mean or suchlike) for a string variable


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: AW: egen(mean or suchlike) for a string variable
Date   Thu, 8 Oct 2009 17:23:15 +0100

Let's underline that this can all be done with strings. There is no need to resort to -encode- or otherwise to convert to numeric. 

Missing, i.e. empty, strings sort first. Thus after -input- and -trim()-, Martin's code can be slimmed to 

bys year Prof (Uni) : replace Uni = Uni[_N] if missing(Uni) 

-- without any need for an extra variable. 

However, there is no check here for different non-missing values within groups of -year Prof-. 

In the same territory, note that -egen, mode()- takes string arguments as well as numeric, so can be used for imputation. However, the direct route that Martin exemplifies has many advantages. 

Nick 
n.j.cox@durham.ac.uk 

Martin Weiss

*************
clear*

inp year str10(Uni Prof)
1990  Harvard   " S Smith"
1990   ""      "S Smith"
1990  UCLA      "P Williams"
1990  Yale       " K John"
1991   ""        "K Evert"
1991  Oxford     "K Evert"
1991  "" 	"K Evert"
end

replace Uni=trim(Uni)
replace Prof=trim(Prof)
compress

gen byte nonmiss=!mi(Uni)

//replace with last obs
bys year Prof (nonmiss): /* 
*/ replace Uni=Uni[_N]  /* 
*/ if nonmiss==0

l, noo sepby(year Prof)
*************

joe j

Thanks. (Your suggestion helped me create a variable that takes a
numeric value, instead of the university name; this is definitely an
improvement.)

This is how the data looks like:

Year  University Professor

1990  Harvard    S Smith
1990   ---------     S Smith
1990  UCLA      P Williams
1990  Yale        K John

1991   ---------    K Evert
1991  Oxford     K Evert

What I want is to replace the missing names above, in 1990 with
Harvard and in 1991 with Oxford.

On Thu, Oct 8, 2009 at 11:59 AM, Martin Weiss <martin.weiss1@gmx.de> 

> You should turn the string into a numeric variable via -encode-. Then
-egen-
> can go to work. Also provide an excerpt of your data and show what you
want
> to happen to them...

joe j

> In my data I have a string variable "University", which lists
> university names. In some years the names are missing. Two other
> variables I've are "Professor" and "Year". The same "Professor" and
> "University" can occur multiple times in a year.
>
> The problem I have is that there are quite a few University names that
> are missing. What I want to do is to replace as many missing
> University names as possible, by assuming that: when a professor is
> linked to a university at least once in a year, she is linked to the
> same university during that year - so the missing university name when
> her name occurs again in the same year can be replaced (why there are
> missing university names is a complicated story:)).

> I tried the following in Stata (it's foolish, I know):
>
>  bysort year professor: egen University_all=mean(University)
>
> But I get the warning "type mismatch".

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