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RE: st: Problem with adding 3 numbers


From   "Kanter, Rebecca" <rkanter@jhsph.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Problem with adding 3 numbers
Date   Sat, 17 Oct 2009 00:29:58 -0400

Thanks, Stas! That solved it! Hopefully others will find this helpful as well!
___________________________________________
Rebecca M. Kanter
PhD Candidate
Johns Hopkins Bloomberg School of Public Health
Department of International Health
Center for Human Nutrition
________________________________________
From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of Stas Kolenikov [skolenik@gmail.com]
Sent: Friday, October 16, 2009 11:09 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Problem with adding 3 numbers

Read on -help datatypes- to figure out the relative accuracy of the
stored numbers. The default -float- type (which is a terrible default
if you ask me) stores numbers with about 4e-8 relative accuracy. Your
multiplication by 1e7 produces results accurate to the -state- level
only; your localities are well below the round-off error for this
type. I have forgotten about these troubles ages ago after putting a
line

set type double

into my profile.do file in Stata directory.

On the other hand, a -double- type variable still makes a rather poor
identifier, so you might want to -generate- your compound ID variables
as -long-:

gen long claveloc =((state*10000000)+ (mun2*10000))+loc2

Again, make sure you are still able to store all the numbers
accurately, and the largest ID you could ever need does not exceed
~2bln:

. di %12.0g c(maxlong)
  2147483620

If you have fewer than 214 states, you should be good to go with -long- :))

On Fri, Oct 16, 2009 at 9:27 PM, Kanter, Rebecca <rkanter@jhsph.edu> wrote:
> Hi,
>
> I am trying to add three numbers (1-2 digit code for state plus 3 digit code for municipality + 4 digit code for locality). together unique for each state in a country. I have tried this various ways and each time, after the 1st state, STATA starts to round (I think) some of the numbers. I have tried this numerous ways. No state, municipality, or locality are missing. State is byte. Municipality and locality are strings (that I convert to numeric see below).
>
> gen munloc=mun+loc
> destring munloc, generate(test)
> generate ent2=ent*10000000
> generate claveloc=ent2+test
>
> or whereby:
> mun2=real(mun)
> loc2=real(loc)
> gen claveloc =((state*10000000)+ (mun2*10000))+loc2
>
> ****Anyway I try this, I get problems like this:
>
> state      mun   loc             munloc  test        state2             claveloc
>      2         001     0001    0010001 10001   20000000        20010000 (should be 20010001)
>   ent  mun      loc        munloc              test               state2                claveloc
>    2             001 0139      0010139 10139   20000000        20010140 (should be 20010139)
>
> *Should be like this:
>
> state             mun loc                 munloc        test                  state2    claveloc
> 1                     001       0001    0010001 10001   10000000        10010001
>
>
>
> Can someone please help me get this to work correctly.
>
> Thank you so much,
> Rebecca
>
>
> ___________________________________________
> Rebecca M. Kanter
> PhD Candidate
> Johns Hopkins Bloomberg School of Public Health
> Department of International Health
> Center for Human Nutrition
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>



--
Stas Kolenikov, also found at http://stas.kolenikov.name
Small print: I use this email account for mailing lists only.

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