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# Re: st: RE: foreach and levels of string variable

 From "Paul O'Brien" To statalist@hsphsun2.harvard.edu Subject Re: st: RE: foreach and levels of string variable Date Tue, 28 Sep 2010 08:43:44 +0100

```thanks nick,

this is getting a bit complicated for me.

to avoid the problem you refer to, i could, of course, do a simple logistic on each study.

but it does not seem to recognise the foreach, just repeats the same analysis of the whole dataset.

. levelsof study, local(levelstud)
`"Creinin 2006"' `"Glasier 2010"' `"Hamoda 2004"' `"Ho&Kwan 1993"' `"WHO 1998"' `"von Hertzen 2002"'

. foreach l of local levelstud {
2. logistic p day[fw=pop]
3. }

Logistic regression                               Number of obs   =       6755
LR chi2(1)      =       4.34
Prob > chi2     =     0.0373
Log likelihood =  -604.4323                       Pseudo R2       =     0.0036

------------------------------------------------------------------------------
p | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
day |   1.198313   .1013991     2.14   0.033      1.01518    1.414482
------------------------------------------------------------------------------

Logistic regression                               Number of obs   =       6755
LR chi2(1)      =       4.34
Prob > chi2     =     0.0373

paul

On 27 Sep 2010, at 22:27, Nick Cox wrote:

> Here's a fix for you (better than that in the FAQ cited just below):
>
> egen group = group(study), label
> su group, meanonly
>
> forval i = 1/`r(max)' {
> 	di "`: label (group) `i''"
> 	ptrend p1 np1 day if group == `i'
> }
>
> This strategy is covered by the FAQ you cited at the beginning of this thread.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Nick Cox
>
> I got it. You are now being bitten by an old misfeature. See another Stata FAQ:
>
> Why does a program defined by an ado-file sometimes not work when given a string comparison?
>
> <http://www.stata.com/support/faqs/lang/define.html>
>
> Note that you should have spelled out, as requested by the FAQ, that you were using a user-written program. -ptrend- on SSC is written for Stata 4.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Nick Cox
>
> This works for me:
>
> . clear
>
> . set obs 10
> obs was 0, now 10
>
> . gen which = cond(_n < 6, "some stuff", "other stuff")
>
> . gen y = _n
>
> . levelsof which, local(levels)
> `"other stuff"' `"some stuff"'
>
> . foreach l of local levels {
>  2. su y if which == "`l'"
>  3. }
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>           y |         5           8    1.581139          6         10
>
>    Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>           y |         5           3    1.581139          1          5
>
> I can't see what you're doing wrong. The code looks right. Are you doing something weird like running code from a do-file editor and the interactive session in combination?
>
> paul o'brien
>
> thanks martin and neil with the advice on adding quotes. however, i
> still get the same error:
>
> . levelsof study, local(levelstud)
> `"Ashok 2002"' `"Creinin 2006"' `"Ellertson 2003"' `"Fine 2010"'
> `"Glasier 2010"' `"Hamoda 2004"' `"Ho&Kwan 1993"' `"WHO 19
>> 98"' `"von Hertzen 2002"'
>
> . foreach l of local levelstud {
>   2. ptrend p1 np1 day if study == "`l'"
>   3. }
> Ashok not found
> r(111);
>
> removed " 2002" in "Ashok 2002" and others - same problem.
>
> On 27 September 2010 11:42, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
>>
>> --- On Mon, 27/9/10, Paul O'Brien wrote:
>>> . levelsof study, local(levelstud)
>>>
>>> . foreach l of local levelstud {
>>>   2. ptrend p1 np1 day if study == `l'
>>>   3. }
>>> Ashok not found
>>> r(111);
>>>
>>> where am i going wrong?
>>
>> ptrend p1 np1 day if study == `l'
>>
>> should be
>>
>> ptrend p1 np1 day if study == "`l'"
>>
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/

-------------------------------
Dr Paul O'Brien
Raymede Clinic
Westside Contraceptive Services
Central London Community Healthcare
Exmoor St
London
W10 6DZ
UK
+44 (0)20 8962 4450

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```

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