Date: Thu, 25 Jul 2002 16:53:15 -0400
Reply-To: Ian Whitlock <WHITLOI1@WESTAT.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Ian Whitlock <WHITLOI1@WESTAT.COM>
Subject: Re: Double Assignment
Content-Type: text/plain; charset="iso-8859-1"
Jess,
var2=var3=7
is short for
(var2 = var3) and (var3 = 7)
I see no reason why VAR2 should always be missing, but if it is then the
result is 0 because a logical consequence (transitivity of equality) of the
above expression is that
var2 = 7
and this is never true when VAR2 is missing.
Never trust what a programmer, or anyone else, tells you. Test it, decide
for yourself, and be prepared to revise your opinion when more data is
available to you. Of course even if you find that every example you
consider leads to the truth of the statement you might wonder if SAS would
give the same results tomorrow. If that is true it is time to take up
another language or occupation. (However, note there are exceptions which
may be allowed. Remember the result of some code can depend on the data,
the operating system, the environment (both the out of disk space variety
and magnets) as well as the language.)
However you must also understand things like (run under winows 98 SAS 8.2)
1602 data _null_ ;
1603 x = 7 ;
1604 y = 7 + 4.44e-16 ;
1605 z = x = y ;
1606 put z = ;
1607 run ;
z=1
The search for truth will always depend on what facts you find and your
theoretical model of how to understand those facts.
IanWhitlock@westat.com
-----Original Message-----
From: Balint, Jess [mailto:JBalint@ALLDATA.NET]
Sent: Thursday, July 25, 2002 3:48 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Double Assignment
How exactly would that work out?
var2 is always missing?!?
-----Original Message-----
From: Sigurd Hermansen [mailto:HERMANS1@WESTAT.COM]
Sent: Thursday, July 25, 2002 3:41 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Double Assignment
I would not trust a programmer who leaves out the parentheses. What rules of
operator precedence apply in multiple assignments across the same operator?
Try to explain how SAS will evaluate
var1=var2=var3=7;
to someone other than a committed (or soon to be) SAS programmer!
Sig
-----Original Message-----
From: Jack Hamilton [mailto:JackHamilton@FIRSTHEALTH.COM]
Sent: Thursday, July 25, 2002 3:22 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Double Assignment
Do you mean you have a hard time trusting this, i.e., that it will
produce the answer of 0 or 1 correctly, or that you have a hard time
believing that that's what the statement means?
Why don't you trust or believe it? Has something happened to make you
think it doesn't work that way?
Will it help if you think of it as
var = (var1 = 7)
?
--
JackHamilton@FirstHealth.com
Manager, Technical Development
METRICS Department, First Health
West Sacramento, California USA
>>> "Balint, Jess" <JBalint@ALLDATA.NET> 07/25/2002 11:54 AM >>>
Hello all. I have seen people here write code like "var2 = var1 = 7".
From
what they say var2 = 1 if var1 = 7 and var2 = 0 otherwise. I have a
hard
time trusting this. Is it correct though? Thanks.
Jess
