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Re: st: how do i increment a counter


From   "aine dooley" <acd4983@hotmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: how do i increment a counter
Date   Wed, 31 Aug 2005 14:22:11 -0700

Thanks so much for taking the time to reply.

You are right, my example wasn't the best.

What I am actually trying to do is loop through a list of 6500 patients. Each patient has an exposure_time i.e. the period of time in days during which they are at risk for a fracture. For each age category (see below), I want to add up a cumulative time at risk. So for ages 51-75, I want to come out with a number that contains the total exposure_time for all patient in that age category.

I think numlist apparently only allows 1600 observations which is somehow incremented by using numlist, max('totobs`) though I haven't figured out the syntax.

I'm sure there is a more elegant way to do this, however ...

local age1_sum=0
local age2_sum=0
local age3_sum=0
local age4_sum=0
local totobs = _N

foreach obs of numlist 1/`totobs' {
if age[`obs']<=50 {
local age1_sum = `age1_sum' + exposure_time[`obs']
}
else if age[`obs'] >50 & age[`obs'] <= 75 {
local age2_sum = `age2_sum' + exposure_time[`obs']
}
else if age[`obs'] >75 & age[`obs'] <= 90 {
local age3_sum = `age3_sum' + exposure_time[`obs']
}
else local age4_sum = `age4_sum' + exposure_time[`obs']
}


-Annemarie
University of Washington, Seattle


From: Christian Holz <statalist@krueschan.de>
Reply-To: statalist@hsphsun2.harvard.edu
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: how do i increment a counter
Date: Wed, 31 Aug 2005 21:03:09 +0100

Annemarie,

you should also check the syntax of the if command (-help ifcmd-). The command that you want to be executed if the if statement is true should be either follow on the same line as the "if" or should be enclosed by { }.

That still does not, however, solve the problem, that your code looks quite confused.
In addition to Neil's interpretations of what you might want to achieve, it might also be to get a sum of the age of all observations in your dataset that are over 50 (assuming your age variable is "age"). In that case you could do

local total_sum=0
local totobs = _N

foreach obs of numlist 1/`totobs' {
if age[`obs']>50 {
local total_sum = `total_sum' + age[`obs']
}
}
di `total_sum'
generate total_sum=`total_sum'


C.

---
Christian Holz
Department of Sociology
University of Glasgow
Scotland, U.K.

aine dooley wrote:

I am finding in Stata that there does not seem to be an easy way to increment a counter despite countless trys and readings of the manal.

I want to do something llike the following, this is just an example:

generate byte total_sum =0

for each variable of varlist {
if age > 50
total_sum = total_sum + age
}

Stata doesn't seem to allow the if... then construct unless it is in a program. Although I have written a simple program (crazy that I have to do this) passing arguments, I still can't get it to work.

I must be missing something.

-Annemarie

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