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Re: st: RE: Re: local macro with if qualifier


From   Sabrina Carrossa <carrossa@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Re: local macro with if qualifier
Date   Wed, 8 Apr 2009 17:47:23 +0200

Dear all,
i am really sorry for my question. It was generic and it was not about
syntax-problem
Basically, I did a logic error.
As prof. Pisati wrote me – in a private conversation – I can’t assign
to a scalar a specific value in respect of the values of a variables
(it is impossible). He suggest me to find a new algorithm, and I did
it.
Here the solution.

My object is to find the best friend among a list of friends.
I have a list of  “i” occupation (in the db they are 20, in the
example just 3). For each occupation in the db I have the variables:
- d31b_i : do you have a friend that have the occupation “i”? (yes/no)
- d31c_i: how many time do you spend with this person in the
occupation “i”? (0/6, with 6 a lot of time)
-  d31d_i: how do you feel close with this person in the occupation
“i”? (0/10, with 10 really close)

Than, my idea is that the best friend is a friend with:
- d31b_i=1
- d31c_i= max (among each i)
- d31d_i=max (among each i)
 And, if I have more friends with the same value for these three vars,
the best friend is the friend with higher occupation (max i)

************************************************
* Stata Code:
************************************************

* compute n vars as sum of the information on d31b d31c d31d and occupation (i)
forval i=1/3 {
	gen d31_`i'=0
	replace d31_`i'= (d31b_`i'*100000) + (d31c_`i'*10000) + (d31d_`i'*100) + `i'
}

* in the first step i assign to friend the value of the friend in the
first occupation (i=1)
* than i compare the value of this first friend with the values of the
other friends
* if the values of the other friends are highest (more contact and
more closeness) I replace the value of friend
gen friend=d31_1
gen f=1
forval y=2/3 {
	replace f=`y' if confront<d31_`y'
	replace friend= d31_`y' if confront<d31_`y'
}

I really hope that you can apologize me.
Sincerely,
Sabrina.


2009/4/7 Nick Cox <n.j.cox@durham.ac.uk>:
> How to tackle problems like Sabrina's? Here are suggestions of tactics
> on several levels.
>
> Read help files very closely and carefully
> ==========================================
>
> -help local- indicates allowed syntaxes with -local-. If -if- (or -in-)
> were allowed, that would be explicit in the syntax diagram. It is not.
>
> Only rarely does Stata disguise its syntax and only for good reason!
>
> (It follows, in this case, that Martin's comment about -if- being
> evaluated for the first observation does not apply here. More on that in
> a moment.)
>
> Experiment with simple cases
> ============================
>
> If you're unsure about what a definition implies, experiment with simple
> cases. Let Stata tell you. Here's an illustration:
>
> . sysuse auto
> (1978 Automobile Data)
>
> . local a = 1
>
> . local a = `a' + 1 if mpg == 1
> if not allowed
> r(101);
>
> In short, syntax like this is not allowed. (So, in relation to Martin's
> comment, whether it would do what you want is immaterial.)
>
> Now this is legal:
>
> . local a if mpg == 1
>
> But what is the result?
>
> . di "`a'"
> if mpg == 1
>
> What you typed is just copied as text, without being executed. So this
> strategy is unlikely to be what Sabrina wants.
>
> Illustrate your problem with mutually accessible data
> =====================================================
>
> I just did what anybody can do, as datasets like the -auto- data are
> installed with Stata. The converse should be obvious: we don't have your
> data, which makes it harder to get to the position you are in.
>
> Don't say "it didn't work"; say what happened
> =============================================
>
> I have an evolving private document detailing (so far) 19 different
> senses of "didn't work", collected from Statalist postings. Even Stata
> experts familiar with what you are doing often can't tell what you mean
> when you say "it didn't work". A report like that above makes it
> clearer.
>
> Don't treat Statalist as write-only
> ===================================
>
> Some members of Statalist post only when they have a problem and ignore
> it otherwise. That's understandable, especially as we are all "too
> busy", but it means that those members often miss relevant material.
> Only two hours before Sabrina's posting Ihsuan Li closed a thread in
> which the difference between
>
> if <condition> {
>                <action>
> }
>
> and
>
> <action> if <condition>
>
> was clearly exposed.
>
> State the problem, as well as your failed solution
> ===================================================
>
> As Martin signalled wisely, Sabrina did not explain her problem. My
> instinct is that her code looks way more complicated than her problem is
> likely to require, but I too am too busy to give more time to trying to
> infer what the problem is.
>
> Don't get out of your depth
> ===========================
>
> If you are struggling with Stata basics, writing long complicated code
> is almost never going to work.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Martin Weiss
>
> What exactly are those "d31b_`i'"? If they are variables, then the -if-
> qualifiers are evaluated for the first value only. This may be what you
> want, but experience shows that users are unaware of this more often
> than
> they actually want it. If you could give a description of your data and
> what
> you want to achieve, I am quite sure that you will soon get a much
> easier
> solution...
>
> Sabrina Carrossa
>
>> how can i use a local macro with the if qualifier option?
>> Unfortunately, this code doesn't work:
>>
>> local i=`i'+1 if d31b_`i'!=d31b_`y' & d31b_`i'==0 & `y'<3
>>
>> Thank you in advance.
>>
>> The full code is:
>>
>> gen amico=0
>> local i=1
>> set trace on
>> forval y=2/3 {
>>    replace amico=`i' if d31b_`i'!=d31b_`y' & d31b_`i'==1 & `y'==3
>>    replace amico=`i' if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'>d31c_`y' & `y'==3
>>    replace amico=`i' if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'==d31c_`y' & d31d_`i'>d31d_`y' & `y'==3
>>    replace amico=`i' if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'==d31c_`y' & d31d_`i'==d31d_`y' & `y'==3
>>    replace debug=1 if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'==d31c_`y' & d31d_`i'==d31d_`y' & `y'==3
>>
>>    replace amico=`y' if d31b_`i'!=d31b_`y' & d31b_`i'==0 & `y'==3
>>    replace amico=`y' if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'<d31c_`y' & `y'==3
>>    replace amico=`y' if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'==d31c_`y' & d31d_`i'<d31d_`y' & `y'==3
>>    replace amico=`y' if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'==d31c_`y' & d31d_`i'==d31d_`y' & `y'==3
>>
>>    local i=`i'+1 if d31b_`i'!=d31b_`y' & d31b_`i'==0 & `y'<3
>>    local i=`i'+1 if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'<d31c_`y' & `y'<3
>>    local i=`i'+1 if d31b_`i'==d31b_`y' & d31b_`i'==1 &
>> d31c_`i'==d31c_`y' & d31d_`i'<d31d_`y' & `y'<3
>> }
>> set trace off
>
> *
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>



-- 
sabrina

*
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