Another way to do it:
clonevar work = myvar
qui forval i = 29(-1)1 {
gen myvar_`i' = strpos(work, "`i'") > 0
replace work = subinstr(work, "`i'", "", .)
}
Here 29 is in general whatever highest number you need.
In words, in addition to the -strpos()- logic,
1. Work on a copy, because we're going to change it.
2. Work downwards, from high values down to 1.
3. Once you've checked for a longer string, zap it so that it doesn't
later confuse the search for shorter strings.
Incidentally, don't knock the format (or structure). When Uli Kohler and
I wrote up the tricks we knew for multiple responses (in this sense), it
was pretty clear to us that all such formats or structures have some big
advantages and disadvantages. Our efforts are accessible at
FAQ . . . . . . . . . . . . . . . . . . . Dealing with multiple
responses
. . . . . . . . . . . . . . . . . . . . . . . N. J. Cox and U.
Kohler
4/05 How do I deal with multiple responses?
http://www.stata.com/support/faqs/data/multresp.html
SJ-3-1 pr0008 Speaking Stata: On structure & shape: the case of mult.
resp.
. . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox & U.
Kohler
Q1/03 SJ 3(1):81--99 (no
commands)
discussion of data manipulations for multiple response data
Nick
[email protected]
Jeph Herrin
Solved - this does it:
forv i=1/9 {
gen byte myvar_`i'= regexm(myvar,"^`i':|:`i':|:`i'$")
}
Jeph Herrin wrote:
> I have a dataset in which many variables are in
> the most useless format imaginable. If a question
> has multiple checkboxes as possible answers, the
> response is stored as a string, with a number indicating
> each box checked and these numbers separated by colons.
> Thus:
>
> myvar
> 1:2:3:5:6:7:8:9
> 1:2:3:6
> 1:2:3:4:5:7:8:9
> 1:2:3:5:7:9
> 1:2:3:5:7:8:9
> 2:3:4:6:9
> 1:2:3:5:6:7:8:9
> 1:2:7:8:9
> 7:9
>
> This variable takes 9 values, so I want to split into 9
> different indicator variables, myvar_1-myvar_9, each
> indicating whether that number was selected. -split()-
> does not work, because of the differing number of values
> per string. That is, it produces myvar_1 which equals "7"
> for the last obs.
>
> So I am looking for a way to check whether a given string
> contains a given integer, which would allow me to
>
> forv i=1/9 {
> gen byte myvar_`i'= [`i' is in myvar list]
> }
>
> As long as there are just 9 values, I can use -strpos()-
> to check for the presence of the digit, but some of my variables
> run into tens and twenties, in which case eg searching for "1"
> returns true even if there is only "11".
>
> The only solutions I see are to first -split()- and
> then check all the new indicators, or run through a series of
> checks such as (matches "1:" but not ":1"). I don't like
> either: Is there a direct way to check to see if a given integer
> is in the list?
>
> I think there may be a regex solution, but my Perl programming
> days are so far behind me that I've not been able to come up
> with one.
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