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RE: st: RE: Comparing variables by observation


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Comparing variables by observation
Date   Tue, 21 Sep 2010 21:16:59 +0200

<>

No need for the "[_n]", as Stata compares row by row anyway. 

" gen (1) =" will lead to "invalid name" complaints. Use a better varname...

The -cond()- does not seem to do anything for you there, but then again, we
talked about it in another recent thread...


HTH
Martin


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Anisa Shyti
Sent: Dienstag, 21. September 2010 21:13
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: Comparing variables by observation

I tried the following codes:

by  obscode, sort: gen (1) = cond(5>= X1 & X1>= X2 & X2>=X3 & X3>=4, 1, 0)
by  obscode, sort: gen (2) = cond(X1<=3 & 5<= X3, 1, 0)

I also tried:
gen byte cond2 = X5t[_n] <=3 & X7t[_n] >=5

Is this approach correct? I will try what you both suggest.
Otherwise, I'll have to look for a logical problem..

Thank you very much.
anisa



On Tue, Sep 21, 2010 at 8:57 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> No code of yours allows no comment on that.
>
> Responding to the algebra given, this kind of problem is one in which
Stata's syntax is inescapably long-winded. To save checking on precedence
rules I tend to parenthesise aggressively:
>
> (5 >= X1) & (X1 >= X2) & (X2 >= X3) & (X3 >= 4)
>
> (X1 <= 3) & (5 <= X3)
>
> What you wrote is not illegal but it will be interpreted in terms of 1s
and 0s as explained at length in
>
> http://www.stata.com/support/faqs/data/trueorfalse.html
>
> which will usually yield something quite different from what you want.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Anisa Shyti
>
> I have three variables X1 X2 X3
> (taking values from 1 to 10) and I need to compare their values, by
> observation, according to several conditions (which are theoretically
> derived) of the form, examples: (1) 5>= X1 >=X2 >=X3 >=4; (2) X1<=3
> and 5<= X3.  I need to evaluate each condition on the data by counting
> the number of times it is met, in order to classify the observations.
>
> I tried several approaches, but the total number of classified
> observations exceeds the total number of observations.  So, I am
> guessing I have some redundant counts - maybe I am doing something
> wrong with the coding (given that the conditions are correct).
>
>
> *
> *   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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