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


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: summing up digits and comparing to a check digit
Date   Wed, 15 Mar 2006 16:00:25 -0000

The limitations of the -mod()- function 
given fractional parts are indeed important. 
FWIW, Tom Steichen and I wrote this up at 

http://www.stata.com/support/faqs/data/mod.html

I was presupposing manipulations of integers 
only, as the context implies. 

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

Richard Atkins
 
> 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
 
> >>> 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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