Re: st: Count the number of changing string values

[Nick Cox <njcoxstata@gmail.com>]

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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