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# Re: st: Count the number of changing string values

 From Nick Cox To "statalist@hsphsun2.harvard.edu" Subject Re: st: Count the number of changing string values Date Fri, 14 Jun 2013 13:21:11 +0100

```Fine. If we

tsset id year

and guess at labels  1 No 2 Yes

then Yes after No the previous year is

gen NY = drug == 2 & L.drug == 1

and years of NY are

gen yearNY = year if NY

Yes after No in _any_ previous year can be done too.

Nick
njcoxstata@gmail.com

On 14 June 2013 13:03, Ching Wong <ching.y.wong@student.adelaide.edu.au> wrote:
> The long dataset is as follows:
>
> id sex year drug
> 1   F   1999   Yes
> 1   F   2000   No
> 1   F   2001   Yes
> 1   F   2002     .
> 3   M  1999    No
> 3   M  2000    Yes
> 3   M  2001    Yes
> 3   M  2002    No
> 5   F   1999    Yes
> 5   F   2000    Yes
> 5   F   2001    Yes
> 5   F   2002    Yes
> 10 M   1999    Yes
> 10 M   2000    No
> 10 M   2001    Yes
> 10 M   2002    No
>
> Thanks.
>
> Ching
>
> On 14 June 2013 21:20, Nick Cox <njcoxstata@gmail.com> wrote:
>> Fine. If you tell me what your data are  once -reshape-d I will advise.
>>
>> Nick
>> njcoxstata@gmail.com
>>
>>
>> On 14 June 2013 12:45, Ching Wong <ching.y.wong@student.adelaide.edu.au> wrote:
>>> Hi Nick,
>>>
>>> I would like to count "how many times a user said Yes one year and No the next".
>>>
>>> Thanks.
>>>
>>> Ching
>>>
>>> On 14 June 2013 21:11, Nick Cox <njcoxstata@gmail.com> wrote:
>>>> I take this to be a new question, but I am unclear what you want. Do you want
>>>>
>>>> 1. Counting how many times a user said Yes one year and No the next?
>>>>
>>>> 2. Identifying the first year in which a user said Yes after
>>>> previously saying No.
>>>>
>>>> I fall back on emphasising my previous advice
>>>>
>>>> Long structure ... is likely to be better for you for most analyses.
>>>>
>>>> Get these data -reshape-d. You are going to want to do lots of
>>>> analyses on different kinds of patterns, and keeping this structure is
>>>> really going to strain any user's Stata fluency.
>>>>
>>>> Nick
>>>> njcoxstata@gmail.com
>>>>
>>>>
>>>> On 14 June 2013 12:12, Ching Wong <ching.y.wong@student.adelaide.edu.au> wrote:
>>>>> Thanks Nick
>>>>>
>>>>> Yes, it's all good if I only need to count the first "NO'.
>>>>>
>>>>> But I would rather to see how to count the first "YES & NO" between
>>>>> year of study.
>>>>>
>>>>> id Drug2009   Drug 2000
>>>>> 1    Yes              NO      ------->ONE count
>>>>>
>>>>> Regards,
>>>>>
>>>>> Ching
>>>>>
>>>>> On 14 June 2013 20:24, Nick Cox <njcoxstata@gmail.com> wrote:
>>>>>> I can't see your value labels from here. But suppose that "No" is a
>>>>>> label for value 1.
>>>>>>
>>>>>> replace year = `j' if  Drug`j' == 1 & missing(year)
>>>>>>
>>>>>> I trust that you will be able to modify that to your situation.
>>>>>>
>>>>>>
>>>>>> Nick
>>>>>> njcoxstata@gmail.com
>>>>>>
>>>>>>
>>>>>> On 14 June 2013 11:45, Ching Wong <ching.y.wong@student.adelaide.edu.au> wrote:
>>>>>>> Hi Nick,
>>>>>>>
>>>>>>> So what if -drug*- are numeric variables with value labels, how should
>>>>>>> I change my Command?
>>>>>>>
>>>>>>>
>>>>>>> Thanks!
>>>>>>>
>>>>>>>
>>>>>>> Ching
>>>>>>>
>>>>>>> On 14 June 2013 19:19, Nick Cox <njcoxstata@gmail.com> wrote:
>>>>>>>> Code that "doesn't work" but is not shown can not be commented on.
>>>>>>>> Long structure (I prefer to avoid the word "format" here) is not
>>>>>>>> essential for the problem as I understand it, but it is likely to be
>>>>>>>> better for you for most analyses.
>>>>>>>>
>>>>>>>> The year in which people first said "No" is
>>>>>>>>
>>>>>>>> gen year = .
>>>>>>>>
>>>>>>>> qui forval j = 1999/2012 {
>>>>>>>>         replace year = `j' if  Drug`j' == "No" & missing(year)
>>>>>>>> }
>>>>>>>>
>>>>>>>> tab year
>>>>>>>>
>>>>>>>> So,
>>>>>>>>
>>>>>>>> 1. Everybody starts out with missing.
>>>>>>>>
>>>>>>>> 2. If they said "No" in 1999, -year- is changed to 1999
>>>>>>>>
>>>>>>>> 3. If they said "No" in 2000, -year- is changed to 2000, but only if
>>>>>>>> -year- is missing (so values of 1999 are protected)
>>>>>>>>
>>>>>>>> and so on.
>>>>>>>>
>>>>>>>> You didn't explain your datatypes. If -drug*- are numeric variables
>>>>>>>> with value labels, the syntax will differ accordingly.
>>>>>>>>
>>>>>>>> Nick
>>>>>>>> njcoxstata@gmail.com
>>>>>>>>
>>>>>>>>
>>>>>>>> On 14 June 2013 10:20, Ching Wong <ching.y.wong@student.adelaide.edu.au> wrote:
>>>>>>>>
>>>>>>>>> I have the following data set:
>>>>>>>>>
>>>>>>>>> Id     sex   drug1999   drug2000    drug2001      drug 2001
>>>>>>>>>
>>>>>>>>> 1       F       Yes            No          Yes            Unknown
>>>>>>>>>
>>>>>>>>> 3       M       No           Yes          Yes             No
>>>>>>>>>
>>>>>>>>> 5      F         Yes          Yes          Yes            Yes
>>>>>>>>>
>>>>>>>>> 9      M       Unknown    Yes          No             Yes
>>>>>>>>>
>>>>>>>>> 10     F        Yes           No           Yes             No
>>>>>>>>>
>>>>>>>>> I would like to produce a count of to show the number of people who
>>>>>>>>> quit each year, only count the first time they quit and do not care if
>>>>>>>>> they change their status to ‘No’ again.
>>>>>>>>>
>>>>>>>>> What would be the command? I tried to change it to the long formal and
>>>>>>>>> use the lag function, but it doesn’t work.
>>>>>>>>
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```