Date: Thu, 3 Mar 2005 15:13:16 +0000
Reply-To: toby dunn <tobydunn@HOTMAIL.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: toby dunn <tobydunn@HOTMAIL.COM>
Subject: Re: Tricky conditional execution of do block
In-Reply-To: <MC3-F27ii2dnft1vgvo0006e1df@mc3-f27.hotmail.com>
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Mike,
Glad I could help, but I wouldn't be too embarressed I am the strike out
king as Ron puts, but the more mistakes we make the more we learn. SAS-L
the place where the SAS giants walk and the best SAS school around....
Toby Dunn
From: "Michael Murff" <mjm33@msm1.byu.edu>
Reply-To: <murff@byu.edu>
To: "'toby dunn'" <tobydunn@hotmail.com>
CC: <SAS-L@LISTSERV.UGA.EDU>
Subject: RE: Tricky conditional execution of do block
Date: Thu, 3 Mar 2005 08:06:55 -0700
Okay, now I see. I have used Boolean logic before but I always put a space
such as not (var ge 100), which evaluates to one if true. The proximity of
the () was a style feature I've never seen. I could be embarrassed by my
mistake (again) but I'm having too much fun learning from you guys.
Thanks for the clarification, Toby.
Michael Murff
-----Original Message-----
From: toby dunn [mailto:tobydunn@hotmail.com]
Sent: Thursday, March 03, 2005 7:15 AM
To: mjm33@MSM1.BYU.EDU
Subject: Re: Tricky conditional execution of do block
Mike,
the use of not() below is not a function but a operator, which is used in
comparisions. I found this in the online docs thought you might be
interested.
Logical (Boolean) Operators and Expressions
Logical operators, also called Boolean operators, are usually used in
expressions to link sequences of comparisons. The logical operators are
shown in the following table:
Logical Operators Symbol Mnemonic Equivalent Example
& AND (a>b & c>d)
| OR (table note 1) (a>b or c>d)
! OR
¦ OR
¬ NOT (table note 2) not(a>b)
ˆ NOT
~ NOT
TABLE NOTE 1: The symbol you use for OR depends on your operating
environment.
TABLE NOTE 2: The symbol you use for NOT depends on your operating
environment.
See Order of Evaluation in Compound Expressions for the order in which SAS
evaluates these operators.
In addition, a numeric expression without any logical operators can serve as
a Boolean expression. For an example of Boolean numeric expressions, see
Boolean Numeric Expressions.
----------------------------------------------------------------------------
----
The AND Operator
If both of the quantities linked by AND are 1 (true), then the result of the
AND operation is 1; otherwise, the result is 0. For example, in the
following comparison:
a<b & c>0
the result is true (has a value of 1) only when both A<B and C>0 are 1
(true): that is, when A is less than B and C is positive.
Two comparisons with a common variable linked by AND can be condensed with
an implied AND. For example, the following two subsetting IF statements
produce the same result:
if 16<=age and age<=65;
if 16<=age<=65;
----------------------------------------------------------------------------
----
The OR Operator
If either of the quantities linked by an OR is 1 (true), then the result of
the OR operation is 1 (true); otherwise, the OR operation produces a 0. For
example, consider the following comparison:
a<b|c>0
The result is true (with a value of 1) when A<B is 1 (true) regardless of
the value of C. It is also true when the value of C>0 is 1 (true),
regardless of the values of A and B. Therefore, it is true when either or
both of those relationships hold.
Be careful when using the OR operator with a series of comparisons (in an
IF, SELECT, or WHERE statement, for instance). Remember that only one
comparison in a series of OR comparisons must be true to make a condition
true, and any nonzero, nonmissing constant is always evaluated as true (see
Boolean Numeric Expressions). Therefore, the following subsetting IF
statement is always true:
if x=1 or 2;
SAS first evaluates X=1, and the result can be either true or false;
however, since the 2 is evaluated as nonzero and nonmissing (true), the
entire expression is true. In this statement, however, the condition is not
necessarily true because either comparison can evaluate as true or false:
if x=1 or x=2;
----------------------------------------------------------------------------
----
The NOT Operator
The prefix operator NOT is also a logical operator. The result of putting
NOT in front of a quantity whose value is 0 (false) is 1 (true). That is,
the result of negating a false statement is 1 (true). For example, if X=Y is
0 (false) then NOT(X=Y) is 1 (true). The result of NOT in front of a
quantity whose value is missing is also 1 (true). The result of NOT in front
of a quantity with a nonzero, nonmissing value is 0 (false). That is, the
result of negating a true statement is 0 (false).
For example, the following two expressions are equivalent:
not(name='SMITH')
name ne 'SMITH'
Furthermore, NOT(A&B) is equivalent to NOT A|NOT B, and NOT(A|B) is the same
as NOT A & NOT B. For example, the following two expressions are equivalent:
not(a=b & c>d)
a ne b | c le d
----------------------------------------------------------------------------
----
Boolean Numeric Expressions
In computing terms, a value of true is a 1 and a value of false is a 0. In
SAS, any numeric value other than 0 or missing is true, and a value of 0 or
missing is false. Therefore, a numeric variable or expression can stand
alone in a condition. If its value is a number other than 0 or missing, the
condition is true; if its value is 0 or missing, the condition is false.
0 | . = False
1 = True
For example, suppose that you want to fill in variable REMARKS depending on
whether the value of COST is present for a given observation. You can write
the IF-THEN statement as follows:
if cost then remarks='Ready to budget';
This statement is equivalent to:
if cost ne . and cost ne 0
then remarks='Ready to budget';
A numeric expression can be simply a numeric constant, as follows:
if 5 then do;
The numeric value that is returned by a function is also a valid numeric
expression:
if index(address,'Avenue') then do;
Toby Dunn
From: Michael Murff <mjm33@MSM1.BYU.EDU>
Reply-To: Michael Murff <mjm33@MSM1.BYU.EDU>
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Tricky conditional execution of do block
Date: Wed, 2 Mar 2005 23:33:52 -0700
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FILETIME=[080ECBE0:01C51FBB]
Howard et al.,
My second primer in retain in as many days (thanks Dennis). I have to
say that this one took a few hours to sink in. I had never seen the
likes of the not() function (in SAS) and coundnt' find it in the
official online SAS docs(9.1.3), nor was it in Cody's functions text. I
have to say that I laughed out loud when I tested the following code
(trivial extension).
data _null_;
x=1; y=0;
if not not(x) then put "x=" x;
if not(y) then put "y=" y;
run;
Howard's trick will do the trick for this "tricky" post.
All the best,
Michael Murff
PS--I googled for "SAS boolean functions" and came up blank. Are there
others of the same ilk as not() e.g. boolean and / or (no pun intended
:-) undocumented? My guess is that this function may have been
documented in an earlier version of SAS.
>>> "Howard Schreier <hs AT dc-sug DOT org>" <nospam@HOWLES.COM>
03/02/05 3:11 PM >>>
Since Michael's data set is sorted on VAR, the extra step and extra pass
are avoidable.
Try this:
data test;
input var @@;
cards;
5 26 26 27 28
;
data _null_;
set test;
retain found252627 0;
if var in (25,26,27) and not(found252627) then found252627 = var;
if var=found252627 then put _all_;
run;
I get:
var=26 found252627=26 _ERROR_=0 _N_=2
var=26 found252627=26 _ERROR_=0 _N_=3
On Wed, 2 Mar 2005 09:31:56 -0800, Dennis Diskin <diskin@SNET.NET>
wrote:
>Michael,
>
>There are a number of ways to do this, but I prefer:
>
>proc sql noprint;
>select min(var) into :minvar from yourdata where 25 <= var <= 27;
>Quit;
>
>And then use &minvar in your if statement.
>
>HTH,
>Dennis Diskin
>
>
>Michael Murff <mjm33@MSM1.BYU.EDU> wrote:
>Hi SAS-L,
>
>
>
>I have a dataset sorted on variable, VAR, whose values range from
1-100. I
>want to execute a do block for the all observations were VAR is less
than
or
>equal to the smallest value in the range of 25-27. So if 25 exists I
only
>want to execute the do block for the records having VAR le 25. But if
25
>does not exist then I want to execute the DO block on all records where
VAR
>le 26 or 27, whatever the smallest in the dataset may be. This seems to
me
>to be a rather difficult thing to code in logically. I could come up
with
>some kind of flagging scheme, I guess, and process the datasets before
hand
>and then condition on those flags, but _seems_ like something like this
>could be done in a DO UNTIL or DO WHILE or DO BLOCK.
>
>
>
>Thanks for your patience with me,
>
>
>
>Michael Murff
>
>Provo, UT
