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Re: st: Creating ten 10%-portfolios


From   "Yu Chen, PhD" <profyuchen@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Creating ten 10%-portfolios
Date   Fri, 1 Mar 2013 17:13:04 -0600

If Stata Corp. can improve -xtile- by enabling by: prefix, that will
be much better.



On Fri, Mar 1, 2013 at 2:11 PM, Bo Spiljard <bo.spiljard@gmail.com> wrote:
> Thank you for your solution!
> I was not informed that the -xtile()- function could do this.
> After a couple tries and some fiddling I managed to do it with this function.
>
> It is not the most tidy solution it does the work.
>
> The code I used:
>
>
> gen illiq2=illiq
>
> sort id year month illiq2
>
> quietly by id year month illiq2: gen dup=cond(_N==1,0,_n)
>
> replace illiq2=. if dup>1
>
> xtile temp = illiq2, nq(10)
>
> by id year month: egen portfolio1=max(temp)
>
> drop dup
>
> drop illiq2
>
> drop temp
>
> sort id year month day
>
> On Fri, Mar 1, 2013 at 6:39 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>> It sounds as if you need to check out the -xtile()- function in
>> -egenmore- (SSC).
>>
>> Alternatively, here is a solution from first principles for what I
>> think you are asking, but I have just written this down, not tested
>> it.
>>
>> gen mdate = ym(year month)
>> egen group = group(mdate)
>> su group, meanonly
>> local max = r(max)
>>
>> gen portfolio = .
>>
>> qui forval i  = 1/`max' {
>>         xtile temp=illiq if group == `i'
>>         replace portfolio = temp if group == `i'
>>         drop temp
>> }
>>
>>
>> Nick
>>
>> On Fri, Mar 1, 2013 at 4:00 PM, Bo Spiljard <bo.spiljard@gmail.com> wrote:
>>
>>  I am testing a version of the
>>> CAPM and I need to make ten 10-percentile portfolios (sub groups) and
>>> these have to be revised each month. This has to be done by creating a
>>> new variable that contains the numbers 1 to 10 and each number should
>>> represent a portfolio.
>>>
>>> Normally if I am stuck I could find the answer by searching on
>>> statalist, but this problem I could not find. I allready tried alot of
>>> things myself (i.e. using r(p10)) etc, but I cannot find the right
>>> code. The data I have is: id, date (year, month and day), and illiq. I
>>> need to create 10 equal portfolios based on the proportion of illiq
>>> and this have to be revised each month. So each of the portfolio at
>>> each month has to contain the same amount of ids, with in portfolio 1
>>> the id with the lowest value of illiq, in portfolio 2 the id with
>>> slightly higher illiq, etc..
>>>
>>> Also the data for each firm does not start and not end at the same
>>> date and also for each date there is missing information, so I cannot
>>> purely use the sort function.
>>>
>>> Here is an simplified example with allready portfolios added how it
>>> should look like.
>>>
>>> id            year       month  day        illiq         portfolio
>>>
>>> 1             2001      1             1             15           3
>>>
>>> 2             2001      1             1             13           2
>>>
>>> 3             2001      1             1             12           1
>>>
>>> 1             2001      1             2             11           3
>>>
>>> 2             2001      1             2             8             2
>>>
>>> 3             2001      1             2             13           1
>>>
>>> ...
>>>
>>> 1             2001      2             1             10           3
>>>
>>> 2             2001      2             1             9             2
>>>
>>> 3             2001      2             1             7             1
>>>
>>> ...
>>>
>>> 1             2009      12           31           8             1
>>>
>>> 2             2009      12           31           11           2
>>>
>>> 3             2009      12           31           13           3
>>>
>>>
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