Re: st: RE: Dividing data into quintiles

[Nick Cox <njcoxstata@gmail.com>]

Here is a tweak of David's code. I have not tested this, but I can see
two problems with his code. The -replace- should be restricted to the
observations it was calculated for; otherwise you overwrite good
values with missings. I would not create a new temporary variable each
time round the loop.

gen quintile = .
quietly levelsof yrmonth, local(levs)

quietly foreach lev of local levs {
         xtile work = return if rtype=="formation" & yrmonth == "`lev'", n(5)
         replace quintile = work if rtype=="formation" & yrmonth == "`lev'"
         drop work
 }
>
Nick
njcoxstata@gmail.com


On 28 October 2013 21:33, Clarice Martins <martins.clarice@gmail.com> wrote:
> Hello David, hello all!!
>
> I believe you understood correctly!  Thank you for your suggestion!
>
> But forgive me, if I am totally off, I am very new with Stata: I think I understood your code, but after creating the variable quintile, this one was kept empty. Should I see values recorded on that? Or the results of the code are stored virtually?   (sorry! very basic question!)
>
> In my research, the next step will use returns for the companies in the 1st and 5th quintile of each  -rtype=="formation" & yrmonth == "`lev'"-  for calculations, so I do need to have available these quintiles (specifically 1st and 5th) for next step.
>
> Thank you!!
> Clarice
>
>
>
> On Oct 28, 2013, at 4:58 PM, Radwin, David wrote:
>
>> Clarice,
>>
>> If I understand correctly, you merely need to loop through each value of yrmonth and calculate quintiles for observations with that value for yrmonth. But you can't generate a new variable 151 times.
>>
>> So you could do something this that creates quintiles for a temporary variable:
>>
>> gen quintile = .
>> quietly levelsof yrmonth, local(levs)
>> foreach lev of local levs {
>>       tempvar quint
>>       xtile `quint' = return if rtype=="formation" & yrmonth == "`lev'", n(5)
>>       replace quintile = `quint'
>>       }
>>
>>
>> David
>> --
>> David Radwin
>> Senior Research Associate
>> Education and Workforce Development Division
>> RTI International
>> 2150 Shattuck Ave., Suite 800
>> Berkeley, CA 94704
>> Phone: 510-665-8274
>>
>> www.rti.org
>>
>>
>>> -----Original Message-----
>>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
>>> statalist@hsphsun2.harvard.edu] On Behalf Of Clarice Martins
>>> Sent: Monday, October 28, 2013 11:39 AM
>>> To: statalist@hsphsun2.harvard.edu
>>> Subject: st: Dividing data into quintiles
>>>
>>> Dear group,
>>>
>>> I need to select a sub-group of my dataset and cut it into quintiles, in
>>> order to proceed with calculations with top and bottom quintile.
>>>
>>> - I use Stata 12.1 (for Mac)
>>>
>>> - my data looks like this (now, after considerations from the group, thank
>>> you!)
>>>
>>> co_id ticker rtype   yrmonth return
>>> 1 ABCB formation jun2000 0.01
>>> 1 ABCB buysell jul2000 0.01
>>> 1 ABCB holding ago2000 0.01
>>> 2 AEDU formation jun2000 0.01
>>> 2 AEDU buysell jul2000 0.01
>>> 2 AEDU holding ago2000 0.01
>>> 3 AMBV formation jun2000 0.01
>>> 3 AMBV buysell jul2000 0.01
>>> 3 AMBV holding ago2000 0.01
>>>
>>> - i tryed both -egen cut- and -xtile-
>>>
>>> egen quintile = cut(return) if rtype=="formation", group(5)
>>>
>>> xtile quintile=return if rtype=="formation", n(5)
>>>
>>> - when I use -if rtype=="formation"- both commands work fine!
>>>
>>> - But, I need to select all observations rtype=="formation"  AND
>>> yrmonth=="jun2000", then cut this subgroup into quintiles
>>>
>>> - Then, I need to proceed with this filter/select and cut, for every
>>> yrmonth (151 periods) on my data set
>>>
>>> Any suggestions?
>>>
>>> Thank you very much!
>>>
>>> Clarice
>>
>>
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