1. Introduction
This module will illustrate the general syntax of SAS
procedures. We will use the auto data file, shown below, to illustrate the syntax of SAS
procedures.
DATA auto ; input MAKE $ PRICE MPG REP78 FOREIGN ; DATALINES; AMC 4099 22 3 0 AMC 4749 17 3 0 AMC 3799 22 3 0 Audi 9690 17 5 1 Audi 6295 23 3 1 BMW 9735 25 4 1 Buick 4816 20 3 0 Buick 7827 15 4 0 Buick 5788 18 3 0 Buick 4453 26 3 0 Buick 5189 20 3 0 Buick 10372 16 3 0 Buick 4082 19 3 0 Cad. 11385 14 3 0 Cad. 14500 14 2 0 Cad. 15906 21 3 0 Chev. 3299 29 3 0 Chev. 5705 16 4 0 Chev. 4504 22 3 0 Chev. 5104 22 2 0 Chev. 3667 24 2 0 Chev. 3955 19 3 0 Datsun 6229 23 4 1 Datsun 4589 35 5 1 Datsun 5079 24 4 1 Datsun 8129 21 4 1 ; RUN;
2. Using a procedure with no options
Now, lets have a look at the use of SAS procedures using proc
means as an example. Here we show that it is possible to use proc means with no options at all. By default,SAS uses the last data file created
(i.e., auto) and it provides means for all of the numeric variables in the
data file.
PROC MEANS ; RUN;
Here you see the results of the means procedure from the auto data file.
SAS displays the sample size (N), mean, standard deviation , minimum and maximum for all of the numeric variables.
Variable N Mean Std Dev Minimum Maximum ------------------------------------------------------------------------------ PRICE 26 6651.73 3371.12 3299.00 15906.00 MPG 26 20.9230769 4.7575042 14.0000000 35.0000000 REP78 26 3.2692308 0.7775702 2.0000000 5.0000000 FOREIGN 26 0.2692308 0.4523443 0 1.0000000 ------------------------------------------------------------------------------
3. Using options on the PROC statement
We can use the data= option to tell proc means
to tell SAS what data file will be used to perform the means
procedure. The data= option comes right after proc means. Even though the
data= option is optional, we strongly recommend
using it every time because it avoids errors of omission when you revise your programs.
PROC MEANS DATA=auto; RUN;
As you see, the results are identical to those above.
Variable N Mean Std Dev Minimum Maximum ------------------------------------------------------------------------------ PRICE 26 6651.73 3371.12 3299.00 15906.00 MPG 26 20.9230769 4.7575042 14.0000000 35.0000000 REP78 26 3.2692308 0.7775702 2.0000000 5.0000000 FOREIGN 26 0.2692308 0.4523443 0 1.0000000 ------------------------------------------------------------------------------
We can use the n, mean and std options to
tell proc means that we just want the N, mean and standard
deviation for the data.
PROC MEANS DATA=auto N MEAN STD ; RUN;
The output, shown below, shows just the N, mean, and
standard deviation, just as we requested.
Variable N Mean Std Dev ---------------------------------------------- PRICE 26 6651.73 3371.12 MPG 26 20.9230769 4.7575042 REP78 26 3.2692308 0.7775702 FOREIGN 26 0.2692308 0.4523443 ----------------------------------------------
These examples have shown us that you can have options
on the proc statement, for example after proc means we
used the data= , n, mean and std options.
4. Using additional statements
Proc means also supports additional statements. Here we use the var statement to say which variable(s)
we want SAS to produce means for.
PROC MEANS DATA=auto; VAR price ; RUN;
As you would expect, the output shows the results just
for the variable price.
Analysis Variable : PRICEN Mean Std Dev Minimum Maximum ------------------------------------------------------------------ 26 6651.73 3371.12 3299.00 15906.00 ------------------------------------------------------------------
Here we also use the class statement to
request means broken down by the variable foreign (i.e., foreign and domestic cars).
PROC MEANS DATA=auto; CLASS foreign ; VAR price ; RUN;
As we requested, the means of price are
shown for the two levels of foreign.
Analysis Variable : PRICEN FOREIGN Obs N Mean Std Dev Minimum Maximum ----------------------------------------------------------------------------- 0 19 19 6484.16 3768.46 3299.00 15906.001 7 7 7106.57 2101.83 4589.00 9735.00 -----------------------------------------------------------------------------
These examples have shown that you can have additional
statements with a proc (for example, the var and
class
statements). Each proc has its own set of additional statements that are valid
for that proc.
5. Options on additional statements
It is also possible to have options on the additional
statements lines (the statements after the proc statement). We will illustrate this
using proc reg.
Here we use proc reg to predict price
from mpg. We use the model statement to tell
proc
reg that we want to predict price from mpg.
PROC REG DATA=auto ; MODEL price = mpg ; RUN; QUIT;
Here is the output from the proc reg.
Model: MODEL1
Dependent Variable: PRICE
Analysis of Variance
Sum of Mean
Source DF Squares Square F Value Prob>F
Model 1 54620027.581 54620027.581 5.712 0.0251
Error 24 229491191.53 9562132.9806
C Total 25 284111219.12
Root MSE 3092.26988 R-square 0.1922
Dep Mean 6651.73077 Adj R-sq 0.1586
C.V. 46.48820
Parameter Estimates
Parameter Standard T for H0:
Variable DF Estimate Error Parameter=0 Prob > |T|
INTERCEP 1 13152 2786.6930753 4.720 0.0001
MPG 1 -310.689641 129.99546608 -2.390 0.0251
Notice that we don’t get standardized estimates
(betas). We have to ask proc reg to give those to us. In
particular, we use the stb option on the model
statement, as shown below. Note that the stb option comes after a
forward slash ( / ). Options on a proc statement come right after the name of the proc,
but options for subsequent statements must follow a forward slash.
PROC REG DATA=auto ; MODEL price = mpg / STB; RUN;
The output is the same as the output above, except that
it also includes the portion shown below that has the standardized estimates (betas).
Standardized Variable DF Estimate INTERCEP 1 0.00000000 MPG 1 -0.43846180
6. More examples
We have illustrated the general syntax of SAS procedures
using proc means and proc reg. Let’s look at a few more examples, this
time using proc freq. As you may imagine, proc freq is used for
generating frequency tables. From what we have learned, we would expect that
proc freq
would have:
– Options on the proc freq statement that would influence
the way that the tables look.
– Additional statements that would specify what tables to
produce.
– Options on the additional statements lines that would influence
how those particular tables look.
Let’s examine some examples.
First, consider the program below. As you might
expect, the program below would generate frequency tables for every variable in the auto
data file.
PROC FREQ DATA=auto; RUN;
If we use the page option, proc freq will
start every table on a new page. Note that this influences all of the tables
produced in that proc freq procedure.
PROC FREQ DATA=auto PAGE; RUN;
We have also seen that a SAS procedure can have one or
more optional statements. Below we show that we can have one or more
tables
statements to specify the frequency tables we want, in this case, tables for
rep78
and price. Because we used the page option, each table will start on a
new page. This influences both the tables made for rep78
and price.
(Note that we could have specified tables rep78 price, and gotten the same result,
but we wanted to illustrate having more than one tables statement.)
PROC FREQ DATA=auto PAGE; TABLES rep78 ; TABLES price ; RUN;
As we might expect, we could supply options on each of
the tables statements to determine how those particular tables are
to be shown. The
example below requests frequency tables for rep78 and price, but the table
for rep78 will omit percentages because it used the
nopercent option.
Both tables will appear on a new page (because the page option influences all of
the tables) but only rep78 will suppress the printing of percentages because
the nopercent option only applies to that one tables statement.
PROC FREQ DATA=auto PAGE; TABLES rep78 / NOPERCENT ; TABLES price ; RUN;
7. Problems to look out for
When you use options, it is easy to confuse an option
that goes on the proc statement with options that follow on subsequent statements.
8. For more information
- For a quick reference for the syntax of common SAS
procedures see Overview of SAS Procedures in the SAS Library
. - For an overview of the overall syntax of SAS (not just
procedures), Overview of the SAS Language in the SAS Library
.