Date: Sat, 3 May 1997 11:19:36 EDT
Sender: "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From: Ian Whitlock <whitloi1@WESTATPO.WESTAT.COM>
Subject: Re: ARRAY STATEMENT
Subject: ARRAY STATEMENT
Summary: Arrays allow data values to specify variables.
Respondent: Ian Whitlock <email@example.com>
Terri Harris <taharris@IX.NETCOM.COM> wrote:
>I am an 'experienced' SAS user who must confess to having never used
>an ARRAY statement. Could someone tell me how they use the statement,
>what particular value or advantage as a data step shortcut it offers,
>and so on? Much appreciated, Terri Harris
From an abstract point of view, SAS arrays allow data values to specify
variables. This means that tedious code can often be exchanged by the
introduction of data values to drive the code.
The principle can be important whenever
1) A few lines of code are needed for each variable and there are a
lot of variables.
I have 36 problem flag FLAG1 - FLAG36. Set the flags to 0. I
can write 36 statements
flag1 = 0 ;
flag2 = 0 ;
array flags (36) flag1 - flag36 ;
do i = 1 to dim ( flags ) ;
flag ( i ) = 0 ;
2) The number of variables to change is specified in the data.
N is a number on the input data set. Change the first N flag
variables to 1.
Now I can write 36 statements
if 1 <= n then flag1 = 1 ;
if 2 <= n then flag2 = 1 ;
do i = 1 to n ;
flag ( i ) = 1 ;
3) Which variable is specified in the data.
N2 is a number on the input data set. Change the flag variable
corresponding to this number to 99.
I can write 36 statements
if n2 = 1 then flag1 = 99 ;
if n2 = 2 then flag2 = 99 ;
or I write
flag ( n2 ) = 99 ;
This example if very revealing because it shows that an array
can serve as a master if switch when some condition names the
variable to be changed. I often find simple code cluttered up
with many IF statements can be shortened using arrays because
the IF statements are passing judgement on "is this the variable
I want" instead of going directly to the variable.
In studying the above examples it should be intuitively clear that one
can always eliminate the array at the expense of writing a lot more
"make work" type code when the list of variables is known. Of course
at some point it becomes simpler to learn about arrays.
Two of the three examples above require iterative DO-loops. I would
like to see other examples of array usage that don't involve iterative
DO-loops and conversely examples of iterative DO-loops that don't
Ian Whitlock <firstname.lastname@example.org>