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Re: st: AW: "skipping" missing data

From   Nick Cox <>
Subject   Re: st: AW: "skipping" missing data
Date   Thu, 06 Aug 2009 12:55:09 -0500

Singleton panels are tagged as such by

bysort ptnum : gen allonmyown = _N == 1

Alternatively, panels with two or more are tagged as such by

bysort ptnum : gen twoormore = _N > 1

after which you can go

egen group = group(ptnum) if !missing(bperwk_, wk) & !allonmyown


egen group = group(ptnum) if !missing(bperwk_, wk) & twoormore

B. Timothy Walsh wrote:

Thank you: this worked very nicely.
EXCEPT I now realize I also have instances in which there is only a single data point for an individual. Is there a simple way to modify this line?
egen group = group(ptnum) if !missing(bperwk_, wk)

 > --On Thursday, August 06, 2009 11:28 AM -0500 Nick Cox

Here is one of several alternatives.

generate p1=.
egen group = group(ptnum) if !missing(bperwk_, wk)
summarize group, meanonly

forval i = 1/`r(max)' {
      regress bperwk_ wk if group == `i'
      predict p
      replace p1=p if group == `i'
      drop p

That sets the missings on one side.

See also:

FAQ     . . . . . . . . . . Making foreach go through all values of a
         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
         8/05    Is there a way to tell Stata to try all values of a
                 particular variable in a foreach statement without
                 specifying them?

Despite the reference to -foreach- the FAQ is still pertinent.


Martin Weiss wrote:


You could put it in front of individual commands, or the entire
-forvalues- loop.

B. Timothy Walsh

I am attempting to generate predictions from regressions performed for
each  of a longish list of individuals. The problem is that, for some
individuals, there are no dependent variable data (entries are missing),
so  the regression attempt fails. The problem is that the forvalues loop
then  exits. I would like to somehow "skip" these individuals. Loop
seems to work  fine if there are enough data to perform a regression.
I'd be grateful for  any suggestions.

Here's the code:
generate p1=.
forvalues i = 1/50 {        //50 individuals
    regress bperwk_ wk if ptnum == `i'
    predict p
    replace p1=p if ptnum == `i'
    drop p

I'm pretty much a Stata novice. So, I apologize if I am missing
something  obvious. Using version 10.1.

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