## The Data Step

### Subsetting IF

In a Data Step you can exclude some observations from the dataset with an if statement.

```
data tornados_1980s;
infile FileName;
input year city damages;
* this limits input data to 1980s data;
if 1980 <= year <= 1989;
run;
```

IF .. IN statement
```r
if year in (1980, 1981, 1982);
```
AND, OR
```r
if year = '1980' and city = 'Baltimore';
```
### infile 'filename'

In the data step, import data from a file with the infile command.
```r
data tornados;
infile 'tornados.dat';
input year city cost;
run;
```
### Set

Use the set command to create a new data set from an already created
set.
The following creates a dataset of 1980s tornado data from the larger
set of tornado data.
```r
data tornados_1980s;
set tornados;
if 1980 <= year <= 1989;
run;
```
## The PROC Step

### PROC SORT

The sort procedure, sorts data. You can sort by multiple fields.
Also you can print by a field.
```r
proc sort data=tornados;
by year city;
proc print data=tornados;
by year;
run;
```
### PROC Univariate

PROC Univariate generates descriptive statistics
```r
proc univariate data=tornados;
histogram year;
run;
```
### PROC means

Use proc means when you are only interested in basic descriptive statistics.
### PROC freq

generates tables for data in categories.
### PROC gplot

```r
proc gplot data=tornados;
plot year*cost;
title 'Year by Cost tornados';
run;
```
### PROC corr

#### compute the correlation

```r
proc corr data=grades;
var exam1 exam2 hwscore;
run;
```
### PROC reg

p: prints obs, predicted, residuals
r: same as p, plus more
clm: 95% conf interval for mean of each obs
cli: 95% prediction intervals.
```r
proc reg data=grades;
model final=exam1 hwscore / p r cli clm;
plot final*hwscore;
run;
```
## Multiple Regression Analysis

### Variable Selection

SAS has several methods for selecting variables
```r
proc reg data=cdi;
model y = x1-x8 /selection=rsquare best=1;
model y = x1-x8 /selection=adjrsq best=5;
model y = x1-x8 /selection=cp best=10;
model y = x1-x8 /selection=forward slentry=0.10;
model y = x1-x8 /selection=stepwise slentry=0.10 slstay=0.10;
model y = x1-x8 /selection=backward slstay=0.10;
run;
```
additional pages to try:
<a href=http://www.ats.ucla.edu/stat/sas/modules/graph.htm>more sas</a>