Many Thanks to both Nick Cox & Michael Blasnik for their
suggestions!
On 13 Apr 2004 at 10:43, Nick Cox wrote:
> To expand on a few points:
>
> 1. The -egen- route is naturally fine whenever it
> offers the statistic you want to keep. Note that
> when you go
>
> by person : egen mean = mean(whatever)
>
> That mean will be repeated for every observation
> for each person. For many purposes you will want
> to use each mean just once. Tagging is one way to
> do that
>
> egen tag = tag(person)
>
> tags just one observation for each person. Then
> you can follow up with
>
> ... if tag
>
> If you look inside the -mean()- function you
> will see that it does not use -summarize-.
>
> 2. -statsby- is what I call a reduction command.
> You will get one observation for each person, in your
> problem, i.e. you will lose the existing dataset.
> Roger Newson's set of commands is another
> example of a reduction approach.
>
> 3. Doing it yourself with a loop is not too
> difficult, but you must loop over groups at
> a minimum. One FAQ which may be of help is
> http://www.stata.com/support/faqs/data/foreach.html
>
> Persons will have integer or string identifiers,
> so using -levels- is often effective. Taking
> your program
>
> > program mean_get
> > syntax [varlist]
> > foreach i of local varlist {
> > generate overall2 = 0
> > by name, sort: summarize `i', meanonly
> > local 1 = r(mean)
> > by name, sort: replace overall2 = `1'
> > }
> > end
>
> let's forget that -egen- exists and write a program
> that puts means of a varlist into variables -mean_*-
> for a division by some required variable.
>
> program mean_get
> * NJC after Clint Thompson 13 April 2004
> version 8
> syntax varlist(numeric), by(varname)
>
> // check new names will be OK
> foreach v of local varlist {
> confirm new var mean_`v'
> }
>
> // this will fail if `by' is not categorical
> qui levels `by', local(B)
> capture confirm numeric var `by'
> local isstr = _rc != 0
>
> qui foreach v of local varlist {
> gen mean_`v' = .
> if `isstr' {
> foreach b of local B {
> su `v' if `by' == `"`b'"', meanonly
> replace mean_`v' = r(mean) if `by' == `"`b'"'
> }
> }
> else {
> foreach b of local B {
> su `v' if `by' == `b', meanonly
> replace mean_`v' = r(mean) if `by' == `b'
> }
> }
> }
> end
>
> I added a bit more checking. There is still much that
> could be added e.g. support for -if- and -in-.
>
> Nick
> [email protected]
>
> Michael Blasnik
>
> > most directly:
> >
> > by name: egen overall2=mean(`i')
> >
> > will put the mean of var `i', calculated for each value of name, in
> > overall2. Of course, this value will still be overwritten by the next
> > var in the varlist if your loop is left as shown.
> >
> > More specifically, when you use constructs such as -by x:
> > summ y- , you
> > can't get at the individual results -- it's quite frustrating
> > when you first
> > discover this. Instead you either have to write your own loop across
> > groups, or else you may be able to use an -egen- function or -statsby-
> > (or perhaps -parmby-).
>
> [email protected]
>
> > > Is there a way to save the mean in r() for each value of a
> > > variable? More specifically, I want the mean for each
> > > different person contained within the variable 'name'. My
> > > programming experience in Stata is quite limited so I'd
> > > appreciate any advice; the shrapnel from my attempt at coding
> > > is pasted below:
> > >
> > > program mean_get
> > > syntax [varlist]
> > > foreach i of local varlist {
> > > generate overall2 = 0
> > > by name, sort: summarize `i', meanonly
> > > local 1 = r(mean)
> > > by name, sort: replace overall2 = `1'
> > > }
> > > end
> > >
> > > When I run this, it returns the mean from the last value in
> > > 'name' and uses it to replace all values of 'overall2'. Any
> > > suggestions?
>
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
