st: Re: eliminate negative values and their positive counterpart

["Sergiy Radyakin" <Radyakin@aoek.uni-hannover.de>]

Hello Sara,

you will get a dozen of ways to do this more efficiently in several minutes, 
but here is a straightforward way:

Assume your data is:
   +------------+
    | t   charge |
    |------------|
 1. | 1       10 |
 2. | 2       20 |
 3. | 2       20 |
 4. | 3       30 |
 5. | 3       20 |
    |------------|
 6. | 3      -30 |
 7. | 3      -30 |
 8. | 4       10 |
 9. | 4       20 |
10. | 4       30 |
    |------------|
11. | 4       40 |
12. | 5       10 |
13. | 5       20 |
14. | 5      -10 |
15. | 5      -10 |
    |------------|
16. | 5       10 |
17. | 5       10 |
18. | 5       20 |
19. | 5       10 |
20. | 5       10 |
    |------------|
21. | 5       10 |
22. | 5      -10 |
23. | 5       20 |
24. | 5      -20 |
    +------------+


Then



gen abs_charge=abs(charge)
sort t abs_charge
by t abs_charge:egen npos=count if charge>0

gen posit=1 if charge>0
gen negat=1 if charge<0

by t abs_charge:egen npos=count(posit)
by t abs_charge:egen nneg=count(negat)

by t abs_charge:gen ndel=npos*(npos<nneg)+nneg*(nneg<npos)

by t abs_charge:drop if _n<ndel | _n>_N-ndel


Or something similar? change t as appropriate to define a group.
regards, sergiy




----- Original Message ----- 
From: "sara borelli" <saraborelli77@yahoo.it>
To: <statalist@hsphsun2.harvard.edu>
Sent: Tuesday, March 06, 2007 7:48 PM
Subject: st: eliminate negative values and their positive counterpart



> dear satalist members,
>
> This is an exctract of my data:
>
> personid       charge     proc       date
> 1000124 +13   80048    6/6/2001
> 1000124 +13   80076    6/6/2001
> ...
> 1000124 +13   80048    6/7/2001
> 1000124 +13   80076    6/7/2001
> ...
> 1000124 -13   80048    6/7/2001
> 1000124 -13   80076    6/7/2001
> ...
> 1000124 +13   80048    6/8/2001
> ...
> 1000124 +13   80048    6/9/2001
> ...
> 1000124 +13   81001    6/11/2001
> ...
> 1000124 +13   80048    6/11/2001
> 1000124 +13   80048    6/12/2001
>
> where the dots indicate that other values for the same
> personid are in between. I need to eliminate the
> negative charges AND their positive counterpart with
> the same proc and date. Thus, for example I need to
> eliminate the negative
> -13 80048    6/7/2001
> AND its positive counterpart with the same proc and
> date:
> +13   80048    6/7/2001,
> and so on.
> I should find a way to construct an algorithm that
> identifies and eliminates the negatives AND their
> poistive counterpart with he same date and procedure,
> but I cannot figure that out.
> Any help would be really appreciated
>
> thanks
> Sara Borelli
>
>
>
>
>
>
>
>
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