1 epib 698d lecture 1 notes instructor: raul cruz [email protected] 1/23/2013
TRANSCRIPT
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Syllabus
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What is SAS?
SAS = “Statistical Analysis System” – developed for both data manipulation and data analyses in 1976
Visit the SAS website: http://www.sas.com
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Basics of SAS 5 Windows
EDITOR – file where you write code and comments for execution by SAS (save as .sas)
LOG – file where notes about the execution of the program are written, as well as errors (save as .log)
OUTPUT – file where results from the program are written (save as .lst)
Explorer Window
Results Window
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The SAS interface consists of multiple windows designed for specific functions.
The following windows are open by default:
Enhanced Editor Window
Output Window Log
Window Explorer
Window Results
Window Type SAS programs here. The "enhanced" editor has more advanced features than the traditional "program editor" used in SAS 6.12.
View the results of SAS procedures including tables and line charts. Graphs will be displayed in a separate Graph window.
View SAS programs as they execute including error messages and warnings.
Browse your SAS tables (datasets) and libraries. Create new files and file shortcuts.
Displays a hierarchical outline of SAS results to simplify output navigation.
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SAS Menus File: file input/output Edit: Editing contents in every window
Contents in LOG and OUTPUT windows are not editable, but deletable
View: view programs, log files, outputs, and data sets
Tools: editors for graphics, report, table, etc Solutions: analysis without writing codes Window: navigating among windows Help: help information of SAS
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SAS toolbar
The toolbar gives you quick access to commands that are already accessible through the pull down menus
Not all operating environments have a toolbar
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SAS command bar
Command bar is a place where you can type in SAS command.
Most commands you can type in the command bar are accessible through the SAS menus or the toolbar
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Controlling your windows
The window pull-down menu Type the name of the window in
the command bar Click on the window
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Basic Rules of SAS Codes Every SAS statement ends with a semicolon ; Lines of data are NOT separated by semicolons SAS statements can extend over multiple lines
provided you do not split a word of the statement across lines
More than one statement can appear on a single line
You can start statement anywhere within a line (not recommended)
SAS is case insensitive Words in SAS statement are separated by blanks
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SAS Steps Two main types of SAS steps:
Data Step: read in data, manipulate datasets etc.
PROC Step: perform statistical analyses etc.
DATA and PROC steps execute when a RUN, QUIT, or CARDS statement is enters Another DATA or PROC statement is entered The ENDSAS statement is entered
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SAS Comments Two ways to comment:
/* …..comments…..*/ good for long documentation good for commenting out sections of code
*……comments……; good for commenting out one line of code only commented until first ‘;’
SAS Comments are green in (SAS steps are blue)
Example 1/*Data instructor contains information of several teachers*/
data instructor;input name $ gender $ age;cards;Jane F 30Mary F 29Mike M 28;run;Proc means;var age; run;
SAS Dataset Basic structure: a rectangular matrix
Name Sex Age
Observation 1 Jane F 30
Observation 2 Mary F 29
Observation 3 Mike M 28
Columns are variables Rows are observations
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SAS data type
(1) Numeric data: numbers• Can be added and subtracted• Can have decimal places• Can be positive or negative
(2) Character data: contains letters, numerals or special characters
SAS Dataset and variable names
Dataset name Start with A-Z or underscore character _ Can contain only letters, numbers, or
underscores Can contain upper- and lowercase letters choose names which are easy to be memorized Can be greater than 8 characters in SAS 8.0+
Variable name: same rule as dataset name
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Examples: valid SAS names
Parts LastName First_Name _Null1_ X12 X1Y1
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Examples: invalid SAS names
3Parts Last Name First-Name _Null1$ Num%
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Submitting a program in SAS
First, get your program into the editor
Type your program in the editor Open an existing SAS program: use
open from the File full down menu or use the open icon or just click your SAS program directly
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Submitting a program in SAS
Make your editor window active, and submit your code by
Submit Icon Enter submit in the command bar Select “submit” from the Run pull-
down menu
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Submitting a program in SAS
Reading the SAS log window It starts with notes about the version
of SAS and your SAS site number Original SAS code with line numbers
added on the left Notes contains information about
SAS data set and computer resources used
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Assessing errors in .log file Non-error SAS messages begin with NOTE: SAS error message begin with ERROR: or
possibly WARNING: In data set creation NOTE’s are important to
read because they indicate if the data set was created correctly. Many times there are no errors yet the data set is not correct.
ERROR message sometimes give you hints about options or keywords in DATA/PROC steps
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The output window
Viewing results from the output window
You can save and print contents in the output window
When you have a lot of output, one easy way to find the specific output is to use the list in the “results” window
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SAS Data Libraries A SAS library is simply a location where
SAS data sets are stored Explorer window, click on “libraries”,
there are at least three libraries: Sashelp, Sasuser and work.
Sashelp and Sasuser contains information that controls your SAS session.
Work is the default library, it is a temporary storage location for SAS data sets.
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Creating a new library
Make the “Active libraries” window active (click Explorer, then click libraries)
Choose “New” from the File menu or right click in the active libraries window and choose “New” from the pop-up menu
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Creating a new library Type the name of the library in the box
after name. This name must be eight characters or
fewer, and contains only letters, numbers and underscore.
In the path field, type in the complete path to the folder or directory where you want to save your data (or use Browse)
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Creating a new library
Another way to create a new library is to use the LIBNAME statement to associate the library with a directory accessible from your computer. LIBNAME mylib ‘H:/EPIB698D/week1’;
associates the directory h:/EPIB698D/week1 with the name mylib. Mylib is known as a libref (a library reference)
Temporary/permanent SAS datasets
Every SAS dataset is stored in a SAS data library. By default all data sets created during a SAS session are
temporary data sets and are deleted when you close SAS. All data sets associated with the library WORK are
deleted at the end of the SAS session (they are temporary).
A permanent data set is a data set that will not be deleted when SAS is exited. To create a permanent data set, simply use a different
library name to create a data set.
To create Permanent SAS datasets
Code to create permanent SAS datasets
libname yourlib ‘H:/EPIB698D/week1';
data yourlib.instructor; input name $ sex $ age; cards; Mike M 30 Wendy F 29 Jane F 28 ; run;
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To access Permanent SAS datasets When you start a new SAS session, the
permanent datasets can be accessed directly using libref.
The name of the libref can be different from the name you used when creating the permanent data set.libname mylib ‘H:/EPIB698D/week1';
proc print data=mylib.instructor;
run;
Read existing SAS data: Libname and set statement
libname epib "D:\";
data new;set epib.list_example2;Run;
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Viewing SAS data with SAS Explorer Click the libraries icon in the Explorer
window Click the library you want to see Click the data name to open a SAS
data To go back to the previous window
within Explorer, choose “up one level” from the view menu, or click the up one level button on the toolbar
PROC contents
PROC contents prints the descriptive information about the data set and the variables in the data set Data set information: name, number of
observations, number of variables, and date created
Variable information: name, internal order, type, length, format/informat, and label
Very useful for snapshot a data set Syntax:proc contents data=data_set_name;
run;
TITLES Titles are descriptive headers SAS places at the top of
each page of the OUT window. A title is set with the TITLE statement followed by a
string of character. The string must be enclosed in single or double
quotes. The maximum length for a string is 200 characters. If you want multiple line titles you can use the TITLE
statement where the word title is followed by a number:title1 ‘EPIB 698A'; title2 'week1';
To clear the title setting simply executetitle;
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PROC print The PRINT procedure prints the observations in a SAS
data set to the output window. Features:
Autoformatting columns labeled with variable names or labels automatic accumulation and printing of subtotals
and totals Syntax:
proc print data=data_set_name options;
var var1 var2 var3 var4;
run;
Order
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PROC print (cont.)
Useful options with PROC print: double: double spaces the output noobs: suppresses observation numbers label: uses variable labels as column headings
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PROC print (cont.) The var statement
The var statement is used to specify the variables to process in a proc step. Not unique to proc print.
Variables are usually processed in the order listed in the var statement.
Only applies to a local proc step (not global) If no var statement is used, generally the
procedure will process all the variables (or all the numeric variables if a calculation is performed).
Creating Data in SAS, an overview
Creating datasets by hand entry (Viewtable window, CARDS, DATALINES statement)
Reading dataset from external files (not SAS data, INFILE statement)
Using Import/Export facility (a point-and-click approach)
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Reading Data Inline, CARDS Statement
You enter the actual data points inside the PROGRAM EDITOR
Example: CARDS statement
data instructor;input name $ gender $ age;cards;Jane F 30Mary F 29Mike M 28;run;
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Reading Dataset from External Files: INFILE Statement
Identifies the external file that contains the data and has options that control how the records in file are read into SAS
Must be used before the input statement because it locates the data file to be read
Syntax
data data_set_name;
Infile directory_and_file_name;
input variable_list;
run; 40
Reading raw data separated by spaces—list input
List input (also called free formatted input) can read data separated by at least one space. By default, SAS assumes data values are separated by one or more blanks.
Will read all the data in a record, no skipping unwanted values
Any missing data must by indicated with a period
Character data must be simple, no embedded spaces
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Reading raw data separated by spaces—list input
Example: data demographics; infile ’F:\teaching\SAS\mydata.txt';
input Gender $ Age Height Weight;
run;
$ sign after gender means that gender is a character variable
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Specify missing values with list input
We use a period to represent missing values
M 50 168 155 M 50 168 155
F 23 160 101 F . 160 101 M 65 172 220 M 65 172 220 F 35 165 133 F 35 165 133 M 15 171 166 M 15 171 166
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Reading raw data separated by commas
Comma separated values file (csv file) use commas as data delimiters
They may or may not enclose character values in quotes.
Example: mydata.csv
"M",50,68,155"F",23,60,101"M",65,72,220"F",35,65,133"M",15,71,166
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Reading raw data separated by commas
data demographics; infile 'c:\books\learning\mydata.csv' dsd; input Gender $ Age Height Weight; run;
Dsd: means delimiter sensitive data. It has several functions.(1)change the default delimiter from a blank to a comma.(2)If there are two delimiters in a row, it assumes there is a
missing value in between(3)If character values are placed in quotes, the quotes are
stripped from the value
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INFILE statement, useful options
DSD It recognizes two consecutive delimiters as a
missing value. Example: 20,30,,50, SAS will treat this as 20 30 50 . but with the the dsd option SAS will treat it as 20 30 . 50 .
It allows you to include the delimiter within quoted strings.
Example: a comma separated file and your data included values like "George Bush, Jr.”
With the dsd option, SAS will recognize that the comma in "George Bush, Jr." is part of the name, and not a separator indicating a new variable.
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INFILE statement (cont.)
useful options continued…
obs: specifies the last record to be read into the data set
firstobs: specifies the first line of data to be read into data set. Useful if there is a header row in the dataset.
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data test; infile 'C:\mydata.txt' obs=4 firstobs=2; input Gender $ Age Height Weight;run;
Filename statement
Filename statement identifies the file and associate it with a reference name then use this reference in your INFILE statement instead of the actual file name
Filename datafile'F:\teaching\SAS\mydata.csv';data demographics; infile datafile dsd; input Gender $ Age Height Weight; run;
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Specifying INFILE options with the DATALINES statement
data demographics; infile datalines dsd; input gender $ Age Height Weight;datalines;"M",50,68,155"F",23,60,101"M",65,72,220"F",35,65,133"M",15,71,166;Run;
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Formatted Input
Formatted input can read both character and standard numerical values as well as nonstandard numerical values, such as numbers with dollar signs and commas, and dates.
Formatted input is the most common and powerful of all input methods
SAS Formats and Informats: An informat is a specification for how raw data should be read. A format is a layout specification for how a variable should be printed or displayed. 50
Formatted Input
The w.d informat reads standard numeric values. The w tells SAS how many columns to read; the optional d tells SAS that there is an implied decimal point in the value.
For examples: data value is 123, With informat 3.0, SAS will save it as 123;
With informat 3.1, SAS will save it as 12.3;
If the data value already has a decimal in it, then SAS ignores the d option. For examples: data value is 1.23,
With informat 4.1, SAS will it as 1.23;51
Formatted Input
The $w. Informat tells SAS to read w columns of character data
The MMDDYY10. informat tells SAS that the date you are reading is in the mm/dd/yyyy form. SAS reads the date and converts the value into a SAS date.
SAS stores dates as numeric values equal to the number of days from January 1, 1960. Eg, if you read 01/01/1960, SAS stores a value of 0. The data 01/02/1960 is stored as a value of 1
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The format statement The format statements are built-in SAS command that allow you
to display data in easily readable ways. All SAS formats command ends either in a period or in a period
follows by a number.
title "Listing of FINANCIAL";proc print data=financial;format DOB mmddyy10.
Balance dollar11.2;
The dollar11.2 tells SAS to put a $ sign in front of the number, and allow up to 11 columns to print the balance values, the 2 tells SAS to include two decimal places after the decimal points.
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Using a format/informat statement in a DATA step
It is usually more useful to place your format statement with a SAS data step. There is a permanent association of the formats and variables in the data set.
You can override any permanent format by placing a FORMAT statement in a particular procedure.
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A informat statement with list input
Following the key word informat, you list each variable and information you want to use to read each variable
data list_example; informat Subj $3. Name $20. DOB mmddyy10. Salary dollar8.; infile 'c:\books\learning\list.csv' dsd; input Subj Name DOB Salary; format DOB date9. Salary dollar8.;Run;
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Also helps with the size
of the variable
data list_example;infile 'c:\books\learning\list.csv ' dsd; input Subj : $3. Name : $20. DOB : mmddyy10. Salary : dollar8.; format DOB date9. Salary dollar8.;
there is a colon (called an informat modifier) preceding of each informat. It tells SAS to use informat supplied but to stop reading the values for this variable when a delimiter is met.
Without it, SAS may read past a delimiter to satisfy the width specified in the informat.
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A informat statement with list input (Abbreviated Form)
Import/Export Data
To Export SAS datasets Go to the File menu and select “Export Data” Choose the data file ( from the library Work) Locate and select file type using the browse button Save the data set and finish Check the log to make sure the data set was
created This method does not require a data step, but any
modification may require a data step Convenient for Excel file
Import a SAS data set follows similar step
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Creating and Redefining Variables
You can create and redefine variables with assignment statements as follows: Variable =expression
Type of expression Example
Numeric constant Age =10;
Character constant Gender =‘Female’;
A old variable Age = age_at_baseline ;
Addition Age =age_at_baseline +10;
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Home gardener's data
Gardeners were asked to estimate the pounds they harvested for four corps:tomatoes, zucchini, peas and grapes. Here is the data:
Gregor 10 2 40 0 Molly 15 5 10 1000 Luther 50 10 15 50 Susan 20 0 . 20 Task: add new variable group with a value of 14; add variable type to indicate home gardener; Create a new variable zucchini_1 which equals to
zucchini*10 derive total pounds of corps for each gardener; derive % of tomatoes for each gardener
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Home gardener's data
DATA homegarden;
INFILE 'F:\SAS\lecture4\Garden.txt';
INPUT Name $ 1-7 Tomato Zucchini Peas grapes;
group = 14;
Type = 'home';
Zucchini_1= Zucchini * 10;
Total=tomato + zucchini_1 + peas + grapes;
PerTom = (Tomato / Total) * 100;
Run;
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Home gardener's data
Check the log window: Missing values were generated as a result of performing an operation on missing values.
Since for the last subject, we have missing values for peas, so we the variable total and PerTom, which are calculated from peas, are set to missing
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Exercise 1 Exercise 1 next week
Syllabus is online
Securing SAS outside the classroom Labs (http://www.oit.umd.edu/as/cl/)
Regents Drive Garage (Building #202) in Room 0504. The lab is open 24 hours, 7 days per week: http://www.oit.umd.edu/as/cl/
Desktop version from departments SAS Enterprise