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st: limit to number of digits that can be precisely input into a Stata dataset using -insheet-?


From   "Beede, David N" <dbeede@doc.gov>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: limit to number of digits that can be precisely input into a Stata dataset using -insheet-?
Date   Mon, 14 May 2012 16:50:31 -0400

Is 15 the maximum number of digits one can safely (i.e., precisely) input into a Stata dataset using -insheet-?

I've seen in the statalist archives someone saying that "about 16" is the limit (which I assume is related to the precision for double being 1.414 e-16 (according to the "data types" article in the documentation). 

I'm a little bit nervous because I have been reading in csv file using -insheet- with Census Block identification numbers which are 15 digits long without any apparent problems, but when I used -insheet- to read in an id number that was 19 digits long the resulting Stata dataset did not retain the full 19 digits of precision.

I know this is not a very scientific demonstration, but...


. type test.csv
500019601001002,5000196010010022,50001960100100222,500019601001002222,5000196010010022222

. insheet using test.csv, clear comma nonames
(5 vars, 1 obs)

. 
. forvalues x=1(1)5 {
  2.         local y=`x'+14
  3.         gen str`y' s`x' = string(v`x', "%0`y'.0f")
  4. }

. l s*

     +-----------------------------------------------------------------------------+
  1. |              s1 |               s2 |                s3 |                 s4 |
     | 500019601001002 | 5000196010010022 | 50001960100100224 | 500019601001002240 |
     |-----------------------------------------------------------------------------|
     |                                              s5                             |
     |                             5000196010010021900                             |
     +-----------------------------------------------------------------------------+

David N. Beede, Ph.D.
Economist
Office of the Chief Economist
Economics & Statistics Administration (www.esa.gov)
U.S. Department of Commerce
Office:  Room 4868A
Mailstop:  Room 4858 HCHB
1401 Constitution Avenue, N.W.
Washington, DC  20230
Telephone (202) 482-1226
dbeede@doc.gov 
LinkedIn:  http://www.linkedin.com/in/davidbeede



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