Date:         Mon, 20 Aug 2007 12:45:25 -0700
Reply-To:     "Terjeson, Mark" <Mterjeson@RUSSELL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Terjeson, Mark" <Mterjeson@RUSSELL.COM>
Subject:      Re: Subtracting 2 variables
Comments: To: tanwan <tanwanzang@YAHOO.COM>
In-Reply-To:  A<1187638376.158603.13580@m37g2000prh.googlegroups.com>
Content-Type: text/plain; charset="us-ascii"

Hi Tanwan,

I am going to avoid calling your new
variable as the right_diff because
subtracting number 9 from number 0
is indeed -9, however subtracting 9
from 'nothing' is not necessarily -9.
In your case if that is what you want
then what you are doing is desiring to
have any missings converted from
nothing to zero and then perform your
arithmetic. For that specific purpose
only you can code it like this:


data test;
    input a b;
    wrong_sum = a+b;
    right_sum=sum(a, b);
    wrong_diff=a-b;
    your_diff=max(a,0)-max(b,0);
cards;
1 2
. 9
7 .
;
run;


-or-


data test;
    input a b;
    wrong_sum = a+b;
    right_sum=sum(a, b);
    wrong_diff=a-b;
    your_diff=sum(a,0)-sum(b,0);
cards;
1 2
. 9
7 .
;
run;


-or-


data test;
    input a b;
    wrong_sum = a+b;
    right_sum=sum(a, b);
    wrong_diff=a-b;
    your_diff=sum(a,-b,0);
cards;
1 2
. 9
7 .
;
run;




Hope this is helpful.


Mark Terjeson
Senior Programmer Analyst, IM&R
Russell Investments


Russell Investments
Global Leaders in Multi-Manager Investing








-----Original Message-----
From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of
tanwan
Sent: Monday, August 20, 2007 12:33 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Subtracting 2 variables

When adding,  using '+' may produce wrong results (if some obs are
missing), so one may use the SUM function. Is there a fuction
equivalent to SUM for subtracting, that can handle missing data? As
in:

data;
input a b;
wrong_sum = a+b;
right_sum=sum(a, b);
wrong_diff=a-b;
cards;
1 2
. 9
7 .
;proc print;
run;


I would like to have the right_diff as -1, -9 and 7