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

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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