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st: RE: summing up digits and comparing to a check digit


From   "Richard Atkins" <Richard.Atkins@lshtm.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: summing up digits and comparing to a check digit
Date   Wed, 15 Mar 2006 15:48:20 +0000

Rather than use the mod function I would recommend converting all your
values to formatted strings using the =string(varname, format) command
prior to extracting the digits.

In general the mod function works well but I have come across datasets
where values that displayed in tables and lists as (for example) 0.7
produced a '6' when I tried to extract the 'tenths' digit using
mod(int(varname*10),10).  It turned out that the floating point
representation of this value in the dta file was actually 0.69999999 so
the mod function gave me exactly what I asked for rather than what I
actually wanted.

Some examples of extracting digits in this way are available in my
digit preference functions at
http://www.richardatkins.co.uk/statistics/statabits.htm

Regards

Richard A.
richard.atkins@lshtm.ac.uk 


>>> n.j.cox@durham.ac.uk 03/15/06 3:04 pm >>>
-pnrcheck- from SSC covers the Swedish case. 

In this case, look _inside_ the program 
for some ideas. String functions are not 
the only way. -mod()- is also useful. 

The authors of -pnrcheck- are two Italians
and a Welshman, just who you would expect
to be working on Swedish identifiers. 

Nick 
n.j.cox@durham.ac.uk 

Lia Orfei
 
> I have a variable that contains 7-digit numbers; the first 
> digit is the 
> remainder of the sum of the last six digits divided by 10 
> (check digit)
> 
> example: 1030332 => 0+3+0+3+3+2=11/10=1+1 => check digit=1
>               12050457 => 0+5+0+4+5+7=21/10=2+1 => check digit=1
> and so on.
> 
> Now I want to assess whther the check digit is correct for each
entry.
> 
> How do I calculate the partial sum of the contents of this variable?
> 
> Extra challenge: some of the numbers sum up to 10, 20 etc so 
> the check 
> digit is actually 0 and it does not appear in the data for 
> some reason 
> (example 50456 is correct becasue 5+0+4+5+6=20 so the remainder is
0).
> 
> Any ideas?? I was thinking about using the string functions.

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