MARK CARPENTER, Ph.D.

Transcription

1 MARK CARPENTER, Ph.D. Module 1 : THE DATA STEP (1, 2, 3) Keywords : DATA, INFILE, INPUT, FILENAME, DATALINES Procedures : PRINT Pre-Lecture Preparation: create directory on your local hard drive called i\stat6110\module1. Download SAS programs called Ex1_1.sas, Ex1_2.sas into this directory. Create a raw text file called ex1_1.txt and the comma delimited file ex1_1.csv in this directory, consisting of the following 3 data lines: ex1_1.txt ex1_1.csv ,18, ,21, ,26,98 SAS Programs: module1_examples1.sas and module1_examples2.sas SAS Documenta-on: h"p://support.sas.com/documenta2on/onlinedoc/base/index.html#base94 Slide 1-1

2 DATA step a programming language that you use to manipulate and manage your data. SAS procedures software tools for data analysis and reporting. macro facility a tool for extending and customizing SAS software programs and for reducing text in your programs. DATA step debugger a programming tool that helps you find logic problems in DATA step programs. Output Delivery System (ODS) a system that delivers output in a variety of easy-to-access formats, such as SAS data sets, procedure output files, or Hypertext Markup Language (HTML). SAS windowing environment an interactive, graphical user interface that enables you to easily run and test your SAS programs.

3 The Title of this session is DATA STEP Programming (1, 2, 3). The 1, 2, 3 refers to the three basic elements required in producing a SAS data set in SAS using the DATA STEP process. These three elements are: (1) DATA STEP (begins with a DATA statement and the name of new SAS data set), (2) DATA Source (we use INFILE and FILENAME statements to tell SAS the location and type of data when importing data. A SET statement is used when the source is another SAS data set) (3) DATA Structure: Telling SAS the structure of the data (INPUT, INFOMAT, FORMAT. When the source is an existing SAS data set the INPUT, INFILE, INFORMAT and FILENAME statements are not needed).

4 What is a DATA STEP? The primary method for creating a SAS data set with Base SAS software. A DATA step is a group of SAS language statements that begin with a DATA statement. The group of language statements contains other programming statements that manipulate existing SAS data sets or create SAS data sets from raw data files. A DATA step creates a SAS data set. This data set can be a SAS data file or a SAS view. A SAS data file stores data values while a SAS view stores instructions for retrieving and processing data. When you can use a SAS view as a SAS data file, as is true in most cases, this documentation uses the broader term SAS data set.

5 Some DATA Step Statements (sometimes optional) DATA Statement: Begins a DATA step and provides names for any output SAS data sets, views, or programs. INFILE Statement: Specifies an external file to read with an INPUT statement. Can be used with or without a FILENAME statement (see below) INPUT. Statement: Describes the arrangement of values in the input data record and assigns input values to the corresponding SAS variables FILENAME Statement: Associates a SAS fileref with an external file or an output device, disassociates a fileref and external file, or lists attributes of external files. Can be used for either importing files or exporting files. DATALINES Statement: Specifies that data lines follow for the current DATA STEP. Useful when working with small datasets and SAS programs are being used by more than one person. INFORMATS/FORMAT: Statements Described on next slide.

6 DATA Step when pre-existing SAS DATA used as inputs: All of the above statements are used with importing data from an external source. When you. use a SAS data set as input into a DATA step, the description of the data set is available to SAS. In your DATA step, use a SET, MERGE, MODIFY, or UPDATE statement to read the SAS data set. Use SAS programming statements to process the data and create an output SAS data set.

7 Some DATA Step Statements (cont) INFORMAT AND FORMAT Statements Data and resulting variables come in many types, character, date, numerical, scientific notation. We refer to the format of incoming data from external sources as INFORMATS and the format of variables in SAS data sets as FORMATS. Sometimes it is necessary to specify these during DATA step processing. INFORMAT Statement: specifies any special formats for incoming data during the importation process during a data step. For example, incoming data may have special characters that. SAS uses for other purposes ($,&, etc), date formats will have characters, such as the slash or the month spelled out, etc. The optional INFORMAT Statement tells SAS what to expect with the incoming variables. Note: the format in the resulting data set does not necessarily reflect the incoming format. FORMAT Statement: This specifies the final format of the Data Set produced from a DATA STEP. For example, the date coming in (INFORMAT) might be of the form February 15, 1963, but once the SAS data set is produced (DATA STEP is completed), the format can be changed to 02/15/63.

8 Example 1.1: Simple DATA Steps to import a raw data set containing 3 data lines and 3 variables. To demonstrate different methods, this is done with 6 different DATA steps, example1_1a- f, as described below: Example1_1a: imports from datalines using DATALINES statement. Example1_1b: imports from a raw external data file called ex1_1.txt Example1_1c:. same as above but the external file is located at URL Example1_1d: same as above but adds step of using FILENAME Example1_1e: Uses FILENAME to demonstrate different uses. Example1_1f: Uses SET statement to create SAS dataset from exis2ng SAS set Example1_1g: Uses SET statement to create SAS dataset from exis2ng SAS sets.

9 Example 1.1.a: Simple DATA Step Using DATALINES The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_1a; INFILE DATALINES; DATALINES; ; These lines represent the DATA step that produces the SAS dataset called Example1_1.

10 Example 1.1.a: Simple DATA Step Using DATALINES The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_1a; INFILE DATALINES; DATALINES; ; Begins a DATA step and provides names for any output SAS data sets

11 Example 1.1.a: Simple DATA Step Using DATALINES The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_1a; INFILE DATALINES; DATALINES; ; INFILE usually Specifies an external file to read with an INPUT statement, but in this case it specifies the special case of DATALINES within the datastep.

12 Example 1.1.a: Simple DATA Step Using DATALINES The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_1a; INFILE DATALINES; DATALINES; ; Describes the arrangement of values in the input data record and assigns input values to the corresponding SAS variables.

13 Example 1.1.a: Simple DATA Step Using DATALINES The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_1a; INFILE DATALINES; DATALINES; ; Specifies that data lines follow for the current DATA STEP. Useful when working with small datasets and SAS programs are being used by more than one person.

14 Example 1.1.a: Simple DATA Step Using DATALINES The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_1a; INFILE DATALINES; DATALINES; ; The actual data lines that make up the data to be placed in the final data set. The semicolon must be on the line immediately following the last data line. Note: If the data are contained in a file external to SAS or an existing SAS dataset the DATALINES statement and data would not be needed.

15 Example 1.1.b: Simple DATA Step from external data source The Following DATA step creates a SAS data set called Example1_1b. It produces a data set identical to Example1_1a, but it reads the data from a text file locate on the local harddrive. DATA Step DATA Example1_1b; INFILE i:\stat6110\module1\ex1_1.txt'; RUN;

16 Example 1.1.b: Simple DATA Step from external data source The Following DATA step creates a SAS data set called Example1_1b. It produces a data set identical to Example1_1a, but it reads the data from a text file locate on the local harddrive. Full path name to file on hard drive is in quotes. DATA Example1_1b; INFILE i:stat6110\module1\ex1_1.txt'; RUN;

17 Example 1.1.b: Simple DATA Step from external data source The Following DATA step creates a SAS data set called Example1_1b. It produces a data set identical to Example1_1a, but it reads the data from a text file locate on the local harddrive. DATA Example1_1b; INFILE i:\stat6110\module1\ex1_1.txt'; RUN; Full path name to file on hard drive is in quotes. Note: either single quotes or double quotes (double quotes key on keyboard) will work here. If single quotes used, SAS ignores special reserves characters and treats the string literally. If double quotes, SAS will act if it comes across a SAS reserve characters, like & for a macro variable, for example.

18 Example 1.1.b: Simple DATA Step from external data source The Following DATA step creates a SAS data set called Example1_1b. It produces a data set identical to Example1_1a, but it reads the data from a text file locate on the local hard drive. DATA Example1_1b; INFILE i:\module1\ex1_1.txt'; RUN; RUN not necessary but when SAS reads this statement it officially ends the DATA step statements and SAS begins to process.

19 Example 1.1.c: Simple DATA Step from URL The Following DATA step creates a SAS data set called Example1_1c. It produces a data set identical to Example1_1a & b, but it reads the data from a text file located at the indicated URL. DATA Example1_1c; INFILE ' DEVICE=URL; RUN;

20 Example 1.1.c: Simple DATA Step from URL The Following DATA step creates a SAS data set called Example1_1c. It produces a data set identical to Example1_1a & b, but it reads the data from a text file located at the indicated URL. DATA Example1_1c; INFILE ' DEVICE=URL; RUN; Notice how the DEVICE=URL goes after the quoted string which points SAS to the data file.

21 Example 1.1.d: Simple DATA Step from URL Using FILENAME The Following DATA step creates a SAS data set called Example1_1d. It produces a data set identical to Example1_1a,b, & c, but it reads the data from a text file using the Fileref created with the FILENAME statement. The FILENAME statement associates the name FromWeb with the file located at the indicated URL. Note: SAS must be informed that the file will be found through the indicated URL by including the Keyword URL in the statement. By default SAS assumes the file is located on a local or virtual hard drive. FILENAME FromWeb URL ' ; DATA Example1_1d; INFILE FromWeb; RUN;

22 Example 1.1.e: Using FILENAME for local hard drive The Following DATA step creates a SAS data set called Example1_1e. It produces a data set identical to Example1_1a,b, c & d, but it reads the data from a text file located on the hard drive at the path indicated in quotes. The data step uses the Fileref, FromHD, that was created by the preceding FILENAME Statement. Note: because the file is located on a local hard drive, SAS doesn t have to be informed of any special devices like URL in the previous example. FILENAME FromHD 'i:\stat6110\module1\ex1_1.txt'; DATA Example1_1e; INFILE FromHD; RUN;

23 Example 1.1.f & g: Simple DATA Step from Exis-ng SAS Data Set The Following DATA step creates a SAS data set called Example1_1f from the existing SAS data set Example1_1f using the SET Statement. Example1_1g demonstrates how several SAS data sets can be combined (concatenated) by placing a list of SAS data sets in the SET statement. DATA Example1_1f; SET Example1_1e; RUN; DATA Example1_1g; SET Example1_1a Example1_1b Example1_1c; RUN; The SET and MERGE statements will be covered in greater detail in Module 2 : Combining and Sor2ng SAS Data Sets.

24 DATA Statement Syntax: SAS Documentation indicates several forms (1-6) of DATA steps syntax to reflect different situations, but we only look at the first form here (_null_ data sets, data views, stored programs, passwords, etc, will be discussed later). As Form 1, below indicates, several data sets can be produced during one data step, so to keep it simple for now we examine Revised Form 1syntax. Form 1: DATA <data- set- name- 1 <(data- set- op2ons- 1)> > <...data- set- name- n <(data- set- op2ons- n)> > </ <DEBUG><NESTING><STACK = stack- size> ><NOLIST>; Revised Form 1: DATA <data- set- name <(data- set- op2ons)>>; (data-set-options) specifies optional arguments that the DATA step applies when it writes observations to the output.

25 INFILE Statement Specifies an external file to read with an INPUT statement. Valid in: Category: Type: Opera2ng environment: See: DATA Step File- handling Executable The INFILE statement contains opera2ng environment- specific material. See the SAS documenta2on for your opera2ng environment before using this statement. INFILE Statement under Windows, UNIX, and z/os Syntax INFILE file- specifica2on <device- type><op2ons >; device-type INFILE DBMS- specifica2ons; device-type = specifies the type of device or the access method that is used if the fileref points to an input or output device or location that is not a physical file: FTP, URL, socket, etc. Options: delimiter =, for example, others, file-specification identifies the source of the data, file location, etc.

26 INPUT Statement Describes the arrangement of values in the input data record and assigns input values to the corresponding SAS variables. Valid in: Category: Type: DATA step File- handling Executable Syntax INPUT <specifica2on(s)> Specifica2ons - variable or list of variables, along with informats. Default is numerical (BEST12.) $ - specifies to store the variable value as a character value rather than as a numeric value. Tip: if the variable is previously defined as character, the $ is not necessary.

27 FILENAME Statement Associates a SAS fileref with an external file or an output device, disassociates a fileref and external file, or lists attributes of external files. Valid in: Category: See: Anywhere Data Access FILENAME Statement under Windows, UNIX, and z/os Syntax: FILENAME fileref <device- type> 'external- file' <ENCODING='encoding- value'> <op2ons> <opera2ng- environment- op2ons>; FILENAME fileref <device- type> 'external- file ;

28 FILENAME fileref <device- type> 'external- file ; fileref is any SAS name that you use when you assign a new fileref. Tip: The associa2on between a fileref and an external file lasts only for the dura2on of the SAS session or un2l you change it or discon2nue it by using another FILENAME statement. Change the fileref for a file as ooen as you want. device-type specifies the type of device or the access method that is used if the fileref points to an input or output device or location that is not a physical file. Ex: URL, FTP, etc.

29 Example 1_2 a- g: are repeats of 1_1 a- g but the files are comma delimited The Following DATA step creates a SAS data set called Example1_1a. This data set contains three observations of three numerical variables, ID, Age and Exam1. DATA Example1_2a; INFILE DATALINES delimiter=, ; DATALINES; 1,18,92 2,21,88 3,26,98 ;