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st: RE: Re: Storing output from a loop in only one variable

From   "Nick Cox" <>
To   <>
Subject   st: RE: Re: Storing output from a loop in only one variable
Date   Thu, 8 Jul 2010 17:30:22 +0100

A fairly general recipe is 

gen output = . 
local i = 1 

foreach ... { 
	replace output = ... in `i++' 

su output 

The presumption is that you have enough observations for this to work. 

The `i++' uses the stored value of local macro i, then bumps it up. 

You asked why does 

... in t 

not work, when -t- is a numeric variable. 

-replace- expects to see a literal number or numeric range as the
argument of -in-. 

... in `=t' 

would work as a contraction of `=t[1]' but using local macros as above
is greatly preferable. It would work because the evaluation of `=t'
takes place before -replace- sees the rest of the command line. 

On loops, see for example my namesake's articles

SJ-3-2  pr0009  . . . . . . . . . . . . . Speaking Stata:  Problems with
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q2/03   SJ 3(2):185--202                                 (no
        discusses ways of working through lists held in macros

SJ-2-2  pr0005  . . . . . .  Speaking Stata:  How to face lists with
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q2/02   SJ 2(2):202--222                                 (no
        demonstrates the usefulness of for, foreach, forvalues, and
        local macros for interactive (non programming) tasks


Dani Tilley

Hi Eric,

Thanks for your reply. Unfortunately, this doesn't give me what I'm
looking for. 
With the correction you pointed below, I get an x variable that only has
output from the first loop on ALL its entries. I'm rather looking for a
that has -a- entries (the output from each loop on each line) and -N-a-

Incidentally, could anyone tell me why I'm getting this error:

gen x=.
gen int t=2
replace x=123 in t
't' invalid obs no

what is a valid obs no apart from actual integers plugged in? If I can
out a way to generate a variable that would not trigger this error, I
can then 
replace var=var+i and solve the problem I have.

Eric Booth 

Sorry, that should be "x", not "`x'" in the line:

> replace x = `a' if !mi(`a') & mi(`x')

From: Dani Tilley <>

I'm trying to store certain output in a new variable while I loop
different categories. At the end I want to average what I've stored and
do some other manipulations. Right now, my code looks like this:

foreach a in {range} {
gen x`a'={output} in 1

su x*, mean
di r(mean)
drop x*

So I create `a' variables that have the desired output as their 1st

and N-1 missing points. I then average across these variables and drop
While this gets the job done, I feel it's very clumsy. I'm looking to
create a 
single variable, x, that will hold all `a' outputs. Something like

scalar i=1
foreach a in {range} {
gen x={output} in i
i++ //or i=i+1

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