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Re: st: Generate variable seems to round numbers


From   Carter Rees <carterrees@gmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Generate variable seems to round numbers
Date   Fri, 30 Dec 2011 15:22:29 -0700

Thank you Lars. Your comment prompted me to do a little more digging.
Stata gives me fair warning.

-help data type- leads to the following comment.

"Precision of numeric storage types

    floats have about 7 digits of accuracy; the magnitude of the number
does not matter.  Thus, 1234567 can be stored perfectly as a float, as can
1234567e+20.  The number 123456789, however, would be rounded to
123456792.  In general, this rounding does not matter.

    If you are storing identification numbers, the rounding could matter.
If the identification numbers are integers and take 9 digits or less,
store them as longs; otherwise, store them as doubles.  doubles have 16
digits of accuracy."

I'll have to be more careful.














Hi

Sorry for not giving you an aswere. This was discussed on this list a few
days ago, but i cannot find the string on my phone. Its, as far as i
remember, a presicions problem (se svend juuls book section 5.5 my copy is
at my office) and something to do with how binary code is translated from
and to string values.

Mvh
Lars Folkestad


Den 30/12/2011 kl. 21.21 skrev "Carter Rees" <carterrees@gmail.com>:

> As a follow-up, the new variable ALT_AID_NEW has a format of float %9.0g
> before running the -tostring- command.
> 
> 
> 
> Hi Statalist,
> 
> 
> Working on a Mac Lion, Stata 12 MP4.
> 
> 
> I am working with a data set that has variable ALT_AID stored as long
> %10.0g. The variable is a unique identifier for a best friend the
> respondent named on a survey. ALT_AID was originally stored as an 8
> character string variable but I used -destring- to get it to its present
> format (I didn't specify a format, I let it set to the -destring-
>default).
> 
> My issue is this: If I want to create a duplicate of ALT_AID variable is
> use the command:
> 
> gen ALT_AID_NEW = ALT_AID
> 
> The first case listed in my data set says ALT_AID has a value of
>95576948.
> When I look at the variable ALT_AID_NEW in the editor I see it stored as
> 9.56e+07, clicking on the cell reveals a value of 95576944. If I use the
> -tostring- command it returns an 8 character string variable with the
>same
> value of 95576944. As you can see, my unique identifier is now off by 4
> places in the new variable. This is happening in other cases as well with
> numbers being off by 2 to 4 places.
> 
> I am wondering if this is supposed to be happening and I simply need to
> pay closer attention to formatting decisions in the future. Or, is there
> something amiss with how this being handled in Stata?
> 
> Thank you,
> 
> Carter
> 
> 
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