Re: st: Problem with gen command?

[Richard Goldstein <richgold@ix.netcom.com>]

if you want to make a copy of a variable, use the -clonevar- command

if you must use -gen-, then ensure you set the type to be exactly the
same as the variable you are "copying"

Rich

On 8/7/13 1:51 PM, Stuart Buck wrote:
> Just passing this along from a fellow researcher:
> 
> Be careful with the stata gen command.
> 
> I came across something concerning in stata which I wanted to share.
> I imported some NCES data which brought the ncesid in as a double
> numeric variable.  I wanted to make a duplicate of the ncesid so I
> could do some manipulation without having to preserve/restore or
> reload the data.  When I used: gen ncesid2=ncesid, the values created
> were a float numeric variable and were not equal to those in the
> ncesid variable.
> 
> One of my coworkers and I figured out this was because the float type
> only used 4 bytes so it holds less information than the double type (8
> bytes).  Stata was changing the last few numbers in ncesid2 in order
> to make it fit in the 4 bytes allocated to a float.  The big problem
> is that Stata does not give any notice when it does this. Further, if
> values are being shown in scientific notation, you may not be able to
> see the difference even if you put them side by side.
> 
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