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Re: st: The accuracy of the float data type
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: The accuracy of the float data type
Date
Fri, 24 Jan 2014 16:34:54 +0000
This is very good advice in general, but in this case the maxima are
selected from the original values, so that equality is to be expected
for some observations.
Nick
[email protected]
On 24 January 2014 16:31, Sergiy Radyakin <[email protected]> wrote:
> Zhang, avoid comparing floating point numbers for equality. Instead
> there is a system variable c(epsfloat) , which you can refer to when
> you need to deal with precision:
>
> clear
> input float sales
> 25.395
> 32.007
> end
>
> list
>
> display c(epsfloat)
>
> list if sales==25.395
> list if abs(sales-25.395)<=10*c(epsfloat)
>
> list if sales==32.007
> list if abs(sales-32.007)<=10*c(epsfloat)
>
>
> Best, Sergiy Radyakin
>
> On Fri, Jan 24, 2014 at 11:23 AM, Maarten Buis <[email protected]> wrote:
>> I would do this differently:
>>
>> *------------------ begin example ------------------
>> // get some example data
>> sysuse auto
>>
>> // create a variable denoting missing values
>> gen byte miss = missing(rep78, price)
>>
>> // create our indicator variable
>> bys rep78 miss (price) : gen max = _n == _N if !miss
>>
>> // admire the result
>> list rep78 miss price max in 1/12, sepby(rep78)
>> *------------------- end example -------------------
>> * (For more on examples I sent to the Statalist see:
>> * http://www.maartenbuis.nl/example_faq )
>>
>> Hope this helps,
>> Maarten
>>
>>
>> On Fri, Jan 24, 2014 at 4:53 PM, R Zhang <[email protected]> wrote:
>>> Dear Statalist,
>>>
>>> my data structure is as follows
>>>
>>> firmID segmentID sales year
>>> 1001 1 25.395 1990
>>> 1001 1 32.007 1991
>>>
>>> ............
>>>
>>> a firm can operate in multiple segments as identified by segmentID .
>>> I wanted to identify the largest segment by sales,so I used
>>>
>>> bysort firmID year : egen maxsale=max(sales)
>>>
>>> then I did
>>> gen PriSIC=0
>>> replace PriSIC=1 if sales=maxsale
>>>
>>> I got
>>> firmID segmentID sales year maxsale prisic
>>> 1001 1 25.395 1990 25.395 0
>>> 1001 1 32.007 1991 32.007 0
>>>
>>> I could not figure out why prisic is 0, so I compute the diffderence
>>> (sales-maxsale), it shows a very small negative number , and the data
>>> dictionary shows sales format float %12.0g, and maxsale format float
>>> %9.0g
>>>
>>> what should I do to correct this?
>>>
>>> thanks!!!
>>>
>>> Rochelle
>>> *
>>> * For searches and help try:
>>> * http://www.stata.com/help.cgi?search
>>> * http://www.stata.com/support/faqs/resources/statalist-faq/
>>> * http://www.ats.ucla.edu/stat/stata/
>>
>>
>>
>> --
>> ---------------------------------
>> Maarten L. Buis
>> WZB
>> Reichpietschufer 50
>> 10785 Berlin
>> Germany
>>
>> http://www.maartenbuis.nl
>> ---------------------------------
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/faqs/resources/statalist-faq/
>> * http://www.ats.ucla.edu/stat/stata/
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/faqs/resources/statalist-faq/
> * http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/faqs/resources/statalist-faq/
* http://www.ats.ucla.edu/stat/stata/